using System;
using System.Diagnostics;
using i16 = System.Int16;
using i64 = System.Int64;
using Pgno = System.UInt32;

using sqlite3_int64 = System.Int64;

using u16 = System.UInt16;

using u32 = System.UInt32;

using u8 = System.Byte;

namespace Community.CsharpSqlite
{
	using System.Text;
	using DbPage = Sqlite3.PgHdr;

	public partial class Sqlite3
	{
		/*
		** 2001 September 15
		**
		** The author disclaims copyright to this source code.  In place of
		** a legal notice, here is a blessing:
		**
		**    May you do good and not evil.
		**    May you find forgiveness for yourself and forgive others.
		**    May you share freely, never taking more than you give.
		**
		*************************************************************************
		** This is the implementation of the page cache subsystem or "pager".
		**
		** The pager is used to access a database disk file.  It implements
		** atomic commit and rollback through the use of a journal file that
		** is separate from the database file.  The pager also implements file
		** locking to prevent two processes from writing the same database
		** file simultaneously, or one process from reading the database while
		** another is writing.
		*************************************************************************
		**  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
		**  C#-SQLite is an independent reimplementation of the SQLite software library
		**
		**  SQLITE_SOURCE_ID: 2011-06-23 19:49:22 4374b7e83ea0a3fbc3691f9c0c936272862f32f2
		**
		*************************************************************************
		*/
#if !SQLITE_OMIT_DISKIO
		//#include "sqliteInt.h"
		//#include "wal.h"

		/******************* NOTES ON THE DESIGN OF THE PAGER ************************
		**
		** This comment block describes invariants that hold when using a rollback
		** journal.  These invariants do not apply for journal_mode=WAL,
		** journal_mode=MEMORY, or journal_mode=OFF.
		**
		** Within this comment block, a page is deemed to have been synced
		** automatically as soon as it is written when PRAGMA synchronous=OFF.
		** Otherwise, the page is not synced until the xSync method of the VFS
		** is called successfully on the file containing the page.
		**
		** Definition:  A page of the database file is said to be "overwriteable" if
		** one or more of the following are true about the page:
		**
		**     (a)  The original content of the page as it was at the beginning of
		**          the transaction has been written into the rollback journal and
		**          synced.
		**
		**     (b)  The page was a freelist leaf page at the start of the transaction.
		**
		**     (c)  The page number is greater than the largest page that existed in
		**          the database file at the start of the transaction.
		**
		** (1) A page of the database file is never overwritten unless one of the
		**     following are true:
		**
		**     (a) The page and all other pages on the same sector are overwriteable.
		**
		**     (b) The atomic page write optimization is enabled, and the entire
		**         transaction other than the update of the transaction sequence
		**         number consists of a single page change.
		**
		** (2) The content of a page written into the rollback journal exactly matches
		**     both the content in the database when the rollback journal was written
		**     and the content in the database at the beginning of the current
		**     transaction.
		**
		** (3) Writes to the database file are an integer multiple of the page size
		**     in length and are aligned on a page boundary.
		**
		** (4) Reads from the database file are either aligned on a page boundary and
		**     an integer multiple of the page size in length or are taken from the
		**     first 100 bytes of the database file.
		**
		** (5) All writes to the database file are synced prior to the rollback journal
		**     being deleted, truncated, or zeroed.
		**
		** (6) If a master journal file is used, then all writes to the database file
		**     are synced prior to the master journal being deleted.
		**
		** Definition: Two databases (or the same database at two points it time)
		** are said to be "logically equivalent" if they give the same answer to
		** all queries.  Note in particular the the content of freelist leaf
		** pages can be changed arbitarily without effecting the logical equivalence
		** of the database.
		**
		** (7) At any time, if any subset, including the empty set and the total set,
		**     of the unsynced changes to a rollback journal are removed and the
		**     journal is rolled back, the resulting database file will be logical
		**     equivalent to the database file at the beginning of the transaction.
		**
		** (8) When a transaction is rolled back, the xTruncate method of the VFS
		**     is called to restore the database file to the same size it was at
		**     the beginning of the transaction.  (In some VFSes, the xTruncate
		**     method is a no-op, but that does not change the fact the SQLite will
		**     invoke it.)
		**
		** (9) Whenever the database file is modified, at least one bit in the range
		**     of bytes from 24 through 39 inclusive will be changed prior to releasing
		**     the EXCLUSIVE lock, thus signaling other connections on the same
		**     database to flush their caches.
		**
		** (10) The pattern of bits in bytes 24 through 39 shall not repeat in less
		**      than one billion transactions.
		**
		** (11) A database file is well-formed at the beginning and at the conclusion
		**      of every transaction.
		**
		** (12) An EXCLUSIVE lock is held on the database file when writing to
		**      the database file.
		**
		** (13) A SHARED lock is held on the database file while reading any
		**      content out of the database file.
		**
		******************************************************************************/

		/*
		** Macros for troubleshooting.  Normally turned off
		*/
#if TRACE

static bool sqlite3PagerTrace = false;  /* True to enable tracing */
//#define sqlite3DebugPrintf printf
//#define PAGERTRACE(X)     if( sqlite3PagerTrace ){ sqlite3DebugPrintf X; }
static void PAGERTRACE( string T, params object[] ap ) { if ( sqlite3PagerTrace )sqlite3DebugPrintf( T, ap ); }
#else

		//#define PAGERTRACE(X)
		private static void PAGERTRACE(string T, params object[] ap)
		{
		}

#endif

		/*
** The following two macros are used within the PAGERTRACE() macros above
** to print out file-descriptors.
**
** PAGERID() takes a pointer to a Pager struct as its argument. The
** associated file-descriptor is returned. FILEHANDLEID() takes an sqlite3_file
** struct as its argument.
*/

		//#define PAGERID(p) ((int)(p.fd))
		private static int PAGERID(Pager p)
		{
			return p.GetHashCode();
		}

		//#define FILEHANDLEID(fd) ((int)fd)
		private static int FILEHANDLEID(sqlite3_file fd)
		{
			return fd.GetHashCode();
		}

		/*
		** The Pager.eState variable stores the current 'state' of a pager. A
		** pager may be in any one of the seven states shown in the following
		** state diagram.
		**
		**                            OPEN <------+------+
		**                              |         |      |
		**                              V         |      |
		**               +---------> READER-------+      |
		**               |              |                |
		**               |              V                |
		**               |<-------WRITER_LOCKED------> ERROR
		**               |              |                ^
		**               |              V                |
		**               |<------WRITER_CACHEMOD-------->|
		**               |              |                |
		**               |              V                |
		**               |<-------WRITER_DBMOD---------->|
		**               |              |                |
		**               |              V                |
		**               +<------WRITER_FINISHED-------->+
		**
		**
		** List of state transitions and the C [function] that performs each:
		**
		**   OPEN              -> READER              [sqlite3PagerSharedLock]
		**   READER            -> OPEN                [pager_unlock]
		**
		**   READER            -> WRITER_LOCKED       [sqlite3PagerBegin]
		**   WRITER_LOCKED     -> WRITER_CACHEMOD     [pager_open_journal]
		**   WRITER_CACHEMOD   -> WRITER_DBMOD        [syncJournal]
		**   WRITER_DBMOD      -> WRITER_FINISHED     [sqlite3PagerCommitPhaseOne]
		**   WRITER_***        -> READER              [pager_end_transaction]
		**
		**   WRITER_***        -> ERROR               [pager_error]
		**   ERROR             -> OPEN                [pager_unlock]
		**
		**
		**  OPEN:
		**
		**    The pager starts up in this state. Nothing is guaranteed in this
		**    state - the file may or may not be locked and the database size is
		**    unknown. The database may not be read or written.
		**
		**    * No read or write transaction is active.
		**    * Any lock, or no lock at all, may be held on the database file.
		**    * The dbSize, dbOrigSize and dbFileSize variables may not be trusted.
		**
		**  READER:
		**
		**    In this state all the requirements for reading the database in
		**    rollback (non-WAL) mode are met. Unless the pager is (or recently
		**    was) in exclusive-locking mode, a user-level read transaction is
		**    open. The database size is known in this state.
		**
		**    A connection running with locking_mode=normal enters this state when
		**    it opens a read-transaction on the database and returns to state
		**    OPEN after the read-transaction is completed. However a connection
		**    running in locking_mode=exclusive (including temp databases) remains in
		**    this state even after the read-transaction is closed. The only way
		**    a locking_mode=exclusive connection can transition from READER to OPEN
		**    is via the ERROR state (see below).
		**
		**    * A read transaction may be active (but a write-transaction cannot).
		**    * A SHARED or greater lock is held on the database file.
		**    * The dbSize variable may be trusted (even if a user-level read
		**      transaction is not active). The dbOrigSize and dbFileSize variables
		**      may not be trusted at this point.
		**    * If the database is a WAL database, then the WAL connection is open.
		**    * Even if a read-transaction is not open, it is guaranteed that
		**      there is no hot-journal in the file-system.
		**
		**  WRITER_LOCKED:
		**
		**    The pager moves to this state from READER when a write-transaction
		**    is first opened on the database. In WRITER_LOCKED state, all locks
		**    required to start a write-transaction are held, but no actual
		**    modifications to the cache or database have taken place.
		**
		**    In rollback mode, a RESERVED or (if the transaction was opened with
		**    BEGIN EXCLUSIVE) EXCLUSIVE lock is obtained on the database file when
		**    moving to this state, but the journal file is not written to or opened
		**    to in this state. If the transaction is committed or rolled back while
		**    in WRITER_LOCKED state, all that is required is to unlock the database
		**    file.
		**
		**    IN WAL mode, WalBeginWriteTransaction() is called to lock the log file.
		**    If the connection is running with locking_mode=exclusive, an attempt
		**    is made to obtain an EXCLUSIVE lock on the database file.
		**
		**    * A write transaction is active.
		**    * If the connection is open in rollback-mode, a RESERVED or greater
		**      lock is held on the database file.
		**    * If the connection is open in WAL-mode, a WAL write transaction
		**      is open (i.e. sqlite3WalBeginWriteTransaction() has been successfully
		**      called).
		**    * The dbSize, dbOrigSize and dbFileSize variables are all valid.
		**    * The contents of the pager cache have not been modified.
		**    * The journal file may or may not be open.
		**    * Nothing (not even the first header) has been written to the journal.
		**
		**  WRITER_CACHEMOD:
		**
		**    A pager moves from WRITER_LOCKED state to this state when a page is
		**    first modified by the upper layer. In rollback mode the journal file
		**    is opened (if it is not already open) and a header written to the
		**    start of it. The database file on disk has not been modified.
		**
		**    * A write transaction is active.
		**    * A RESERVED or greater lock is held on the database file.
		**    * The journal file is open and the first header has been written
		**      to it, but the header has not been synced to disk.
		**    * The contents of the page cache have been modified.
		**
		**  WRITER_DBMOD:
		**
		**    The pager transitions from WRITER_CACHEMOD into WRITER_DBMOD state
		**    when it modifies the contents of the database file. WAL connections
		**    never enter this state (since they do not modify the database file,
		**    just the log file).
		**
		**    * A write transaction is active.
		**    * An EXCLUSIVE or greater lock is held on the database file.
		**    * The journal file is open and the first header has been written
		**      and synced to disk.
		**    * The contents of the page cache have been modified (and possibly
		**      written to disk).
		**
		**  WRITER_FINISHED:
		**
		**    It is not possible for a WAL connection to enter this state.
		**
		**    A rollback-mode pager changes to WRITER_FINISHED state from WRITER_DBMOD
		**    state after the entire transaction has been successfully written into the
		**    database file. In this state the transaction may be committed simply
		**    by finalizing the journal file. Once in WRITER_FINISHED state, it is
		**    not possible to modify the database further. At this point, the upper
		**    layer must either commit or rollback the transaction.
		**
		**    * A write transaction is active.
		**    * An EXCLUSIVE or greater lock is held on the database file.
		**    * All writing and syncing of journal and database data has finished.
		**      If no error occured, all that remains is to finalize the journal to
		**      commit the transaction. If an error did occur, the caller will need
		**      to rollback the transaction.
		**
		**  ERROR:
		**
		**    The ERROR state is entered when an IO or disk-full error (including
		**    SQLITE_IOERR_NOMEM) occurs at a point in the code that makes it
		**    difficult to be sure that the in-memory pager state (cache contents,
		**    db size etc.) are consistent with the contents of the file-system.
		**
		**    Temporary pager files may enter the ERROR state, but in-memory pagers
		**    cannot.
		**
		**    For example, if an IO error occurs while performing a rollback,
		**    the contents of the page-cache may be left in an inconsistent state.
		**    At this point it would be dangerous to change back to READER state
		**    (as usually happens after a rollback). Any subsequent readers might
		**    report database corruption (due to the inconsistent cache), and if
		**    they upgrade to writers, they may inadvertently corrupt the database
		**    file. To avoid this hazard, the pager switches into the ERROR state
		**    instead of READER following such an error.
		**
		**    Once it has entered the ERROR state, any attempt to use the pager
		**    to read or write data returns an error. Eventually, once all
		**    outstanding transactions have been abandoned, the pager is able to
		**    transition back to OPEN state, discarding the contents of the
		**    page-cache and any other in-memory state at the same time. Everything
		**    is reloaded from disk (and, if necessary, hot-journal rollback peformed)
		**    when a read-transaction is next opened on the pager (transitioning
		**    the pager into READER state). At that point the system has recovered
		**    from the error.
		**
		**    Specifically, the pager jumps into the ERROR state if:
		**
		**      1. An error occurs while attempting a rollback. This happens in
		**         function sqlite3PagerRollback().
		**
		**      2. An error occurs while attempting to finalize a journal file
		**         following a commit in function sqlite3PagerCommitPhaseTwo().
		**
		**      3. An error occurs while attempting to write to the journal or
		**         database file in function pagerStress() in order to free up
		**         memory.
		**
		**    In other cases, the error is returned to the b-tree layer. The b-tree
		**    layer then attempts a rollback operation. If the error condition
		**    persists, the pager enters the ERROR state via condition (1) above.
		**
		**    Condition (3) is necessary because it can be triggered by a read-only
		**    statement executed within a transaction. In this case, if the error
		**    code were simply returned to the user, the b-tree layer would not
		**    automatically attempt a rollback, as it assumes that an error in a
		**    read-only statement cannot leave the pager in an internally inconsistent
		**    state.
		**
		**    * The Pager.errCode variable is set to something other than SQLITE_OK.
		**    * There are one or more outstanding references to pages (after the
		**      last reference is dropped the pager should move back to OPEN state).
		**    * The pager is not an in-memory pager.
		**
		**
		** Notes:
		**
		**   * A pager is never in WRITER_DBMOD or WRITER_FINISHED state if the
		**     connection is open in WAL mode. A WAL connection is always in one
		**     of the first four states.
		**
		**   * Normally, a connection open in exclusive mode is never in PAGER_OPEN
		**     state. There are two exceptions: immediately after exclusive-mode has
		**     been turned on (and before any read or write transactions are
		**     executed), and when the pager is leaving the "error state".
		**
		**   * See also: assert_pager_state().
		*/

		//#define PAGER_OPEN                  0
		//#define PAGER_READER                1
		//#define PAGER_WRITER_LOCKED         2
		//#define PAGER_WRITER_CACHEMOD       3
		//#define PAGER_WRITER_DBMOD          4
		//#define PAGER_WRITER_FINISHED       5
		//#define PAGER_ERROR                 6
		private const int PAGER_OPEN = 0;

		private const int PAGER_READER = 1;
		private const int PAGER_WRITER_LOCKED = 2;
		private const int PAGER_WRITER_CACHEMOD = 3;
		private const int PAGER_WRITER_DBMOD = 4;
		private const int PAGER_WRITER_FINISHED = 5;
		private const int PAGER_ERROR = 6;

		/*
		** The Pager.eLock variable is almost always set to one of the
		** following locking-states, according to the lock currently held on
		** the database file: NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
		** This variable is kept up to date as locks are taken and released by
		** the pagerLockDb() and pagerUnlockDb() wrappers.
		**
		** If the VFS xLock() or xUnlock() returns an error other than SQLITE_BUSY
		** (i.e. one of the SQLITE_IOERR subtypes), it is not clear whether or not
		** the operation was successful. In these circumstances pagerLockDb() and
		** pagerUnlockDb() take a conservative approach - eLock is always updated
		** when unlocking the file, and only updated when locking the file if the
		** VFS call is successful. This way, the Pager.eLock variable may be set
		** to a less exclusive (lower) value than the lock that is actually held
		** at the system level, but it is never set to a more exclusive value.
		**
		** This is usually safe. If an xUnlock fails or appears to fail, there may
		** be a few redundant xLock() calls or a lock may be held for longer than
		** required, but nothing really goes wrong.
		**
		** The exception is when the database file is unlocked as the pager moves
		** from ERROR to OPEN state. At this point there may be a hot-journal file
		** in the file-system that needs to be rolled back (as part of a OPEN->SHARED
		** transition, by the same pager or any other). If the call to xUnlock()
		** fails at this point and the pager is left holding an EXCLUSIVE lock, this
		** can confuse the call to xCheckReservedLock() call made later as part
		** of hot-journal detection.
		**
		** xCheckReservedLock() is defined as returning true "if there is a RESERVED
		** lock held by this process or any others". So xCheckReservedLock may
		** return true because the caller itself is holding an EXCLUSIVE lock (but
		** doesn't know it because of a previous error in xUnlock). If this happens
		** a hot-journal may be mistaken for a journal being created by an active
		** transaction in another process, causing SQLite to read from the database
		** without rolling it back.
		**
		** To work around this, if a call to xUnlock() fails when unlocking the
		** database in the ERROR state, Pager.eLock is set to UNKNOWN_LOCK. It
		** is only changed back to a real locking state after a successful call
		** to xLock(EXCLUSIVE). Also, the code to do the OPEN->SHARED state transition
		** omits the check for a hot-journal if Pager.eLock is set to UNKNOWN_LOCK
		** lock. Instead, it assumes a hot-journal exists and obtains an EXCLUSIVE
		** lock on the database file before attempting to roll it back. See function
		** PagerSharedLock() for more detail.
		**
		** Pager.eLock may only be set to UNKNOWN_LOCK when the pager is in
		** PAGER_OPEN state.
		*/

		//#define UNKNOWN_LOCK                (EXCLUSIVE_LOCK+1)
		private const int UNKNOWN_LOCK = (EXCLUSIVE_LOCK + 1);

		/*
		** A macro used for invoking the codec if there is one
		*/

		// The E parameter is what executes when there is an error,
		// cannot implement here, since this is not really a macro
		// calling code must be modified to call E when truen

#if SQLITE_HAS_CODEC

		//# define CODEC1(P,D,N,X,E) \
		//if( P.xCodec && P.xCodec(P.pCodec,D,N,X)==0 ){ E; }
		private static bool CODEC1(Pager P, byte[] D, uint N /* page number */, int X /* E (moved to caller */)
		{
			return ((P.xCodec != null) && (P.xCodec(P.pCodec, D, N, X) == null));
		}

		// The E parameter is what executes when there is an error,
		// cannot implement here, since this is not really a macro
		// calling code must be modified to call E when truen

		//# define CODEC2(P,D,N,X,E,O) \
		//if( P.xCodec==0 ){ O=(char*)D; }else \
		//if( (O=(char*)(P.xCodec(P.pCodec,D,N,X)))==0 ){ E; }
		private static bool CODEC2(Pager P, byte[] D, uint N, int X, ref byte[] O)
		{
			if (P.xCodec == null)
			{
				O = D; // do nothing
				return false;
			}
			else
			{
				return ((O = P.xCodec(P.pCodec, D, N, X)) == null);
			}
		}

#else
//# define CODEC1(P,D,N,X,E)   /* NO-OP */
static bool CODEC1 (Pager P, byte[] D, uint N /* page number */, int X /* E (moved to caller */)  { return false; }
//# define CODEC2(P,D,N,X,E,O) O=(char*)D
static bool CODEC2( Pager P, byte[] D, uint N, int X, ref byte[] O ) { O = D; return false; }
#endif

		/*
** The maximum allowed sector size. 64KiB. If the xSectorsize() method
** returns a value larger than this, then MAX_SECTOR_SIZE is used instead.
** This could conceivably cause corruption following a power failure on
** such a system. This is currently an undocumented limit.
*/

		//#define MAX_SECTOR_SIZE 0x10000
		private const int MAX_SECTOR_SIZE = 0x10000;

		/*
		** An instance of the following structure is allocated for each active
		** savepoint and statement transaction in the system. All such structures
		** are stored in the Pager.aSavepoint[] array, which is allocated and
		** resized using sqlite3Realloc().
		**
		** When a savepoint is created, the PagerSavepoint.iHdrOffset field is
		** set to 0. If a journal-header is written into the main journal while
		** the savepoint is active, then iHdrOffset is set to the byte offset
		** immediately following the last journal record written into the main
		** journal before the journal-header. This is required during savepoint
		** rollback (see pagerPlaybackSavepoint()).
		*/

		//typedef struct PagerSavepoint PagerSavepoint;
		public class PagerSavepoint
		{
			public i64 iOffset;                 /* Starting offset in main journal */
			public i64 iHdrOffset;              /* See above */
			public Bitvec pInSavepoint;         /* Set of pages in this savepoint */
			public Pgno nOrig;                  /* Original number of pages in file */
			public Pgno iSubRec;                /* Index of first record in sub-journal */
#if !SQLITE_OMIT_WAL
public u32 aWalData[WAL_SAVEPOINT_NDATA];        /* WAL savepoint context */
#else
			public object aWalData = null;      /* Used for C# convenience */
#endif

			public static implicit operator bool(PagerSavepoint b)
			{
				return (b != null);
			}
		};

		/*
		** A open page cache is an instance of struct Pager. A description of
		** some of the more important member variables follows:
		**
		** eState
		**
		**   The current 'state' of the pager object. See the comment and state
		**   diagram above for a description of the pager state.
		**
		** eLock
		**
		**   For a real on-disk database, the current lock held on the database file -
		**   NO_LOCK, SHARED_LOCK, RESERVED_LOCK or EXCLUSIVE_LOCK.
		**
		**   For a temporary or in-memory database (neither of which require any
		**   locks), this variable is always set to EXCLUSIVE_LOCK. Since such
		**   databases always have Pager.exclusiveMode==1, this tricks the pager
		**   logic into thinking that it already has all the locks it will ever
		**   need (and no reason to release them).
		**
		**   In some (obscure) circumstances, this variable may also be set to
		**   UNKNOWN_LOCK. See the comment above the #define of UNKNOWN_LOCK for
		**   details.
		**
		** changeCountDone
		**
		**   This boolean variable is used to make sure that the change-counter
		**   (the 4-byte header field at byte offset 24 of the database file) is
		**   not updated more often than necessary.
		**
		**   It is set to true when the change-counter field is updated, which
		**   can only happen if an exclusive lock is held on the database file.
		**   It is cleared (set to false) whenever an exclusive lock is
		**   relinquished on the database file. Each time a transaction is committed,
		**   The changeCountDone flag is inspected. If it is true, the work of
		**   updating the change-counter is omitted for the current transaction.
		**
		**   This mechanism means that when running in exclusive mode, a connection
		**   need only update the change-counter once, for the first transaction
		**   committed.
		**
		** setMaster
		**
		**   When PagerCommitPhaseOne() is called to commit a transaction, it may
		**   (or may not) specify a master-journal name to be written into the
		**   journal file before it is synced to disk.
		**
		**   Whether or not a journal file contains a master-journal pointer affects
		**   the way in which the journal file is finalized after the transaction is
		**   committed or rolled back when running in "journal_mode=PERSIST" mode.
		**   If a journal file does not contain a master-journal pointer, it is
		**   finalized by overwriting the first journal header with zeroes. If
		**   it does contain a master-journal pointer the journal file is finalized
		**   by truncating it to zero bytes, just as if the connection were
		**   running in "journal_mode=truncate" mode.
		**
		**   Journal files that contain master journal pointers cannot be finalized
		**   simply by overwriting the first journal-header with zeroes, as the
		**   master journal pointer could interfere with hot-journal rollback of any
		**   subsequently interrupted transaction that reuses the journal file.
		**
		**   The flag is cleared as soon as the journal file is finalized (either
		**   by PagerCommitPhaseTwo or PagerRollback). If an IO error prevents the
		**   journal file from being successfully finalized, the setMaster flag
		**   is cleared anyway (and the pager will move to ERROR state).
		**
		** doNotSpill, doNotSyncSpill
		**
		**   These two boolean variables control the behaviour of cache-spills
		**   (calls made by the pcache module to the pagerStress() routine to
		**   write cached data to the file-system in order to free up memory).
		**
		**   When doNotSpill is non-zero, writing to the database from pagerStress()
		**   is disabled altogether. This is done in a very obscure case that
		**   comes up during savepoint rollback that requires the pcache module
		**   to allocate a new page to prevent the journal file from being written
		**   while it is being traversed by code in pager_playback().
		**
		**   If doNotSyncSpill is non-zero, writing to the database from pagerStress()
		**   is permitted, but syncing the journal file is not. This flag is set
		**   by sqlite3PagerWrite() when the file-system sector-size is larger than
		**   the database page-size in order to prevent a journal sync from happening
		**   in between the journalling of two pages on the same sector.
		**
		** subjInMemory
		**
		**   This is a boolean variable. If true, then any required sub-journal
		**   is opened as an in-memory journal file. If false, then in-memory
		**   sub-journals are only used for in-memory pager files.
		**
		**   This variable is updated by the upper layer each time a new
		**   write-transaction is opened.
		**
		** dbSize, dbOrigSize, dbFileSize
		**
		**   Variable dbSize is set to the number of pages in the database file.
		**   It is valid in PAGER_READER and higher states (all states except for
		**   OPEN and ERROR).
		**
		**   dbSize is set based on the size of the database file, which may be
		**   larger than the size of the database (the value stored at offset
		**   28 of the database header by the btree). If the size of the file
		**   is not an integer multiple of the page-size, the value stored in
		**   dbSize is rounded down (i.e. a 5KB file with 2K page-size has dbSize==2).
		**   Except, any file that is greater than 0 bytes in size is considered
		**   to have at least one page. (i.e. a 1KB file with 2K page-size leads
		**   to dbSize==1).
		**
		**   During a write-transaction, if pages with page-numbers greater than
		**   dbSize are modified in the cache, dbSize is updated accordingly.
		**   Similarly, if the database is truncated using PagerTruncateImage(),
		**   dbSize is updated.
		**
		**   Variables dbOrigSize and dbFileSize are valid in states
		**   PAGER_WRITER_LOCKED and higher. dbOrigSize is a copy of the dbSize
		**   variable at the start of the transaction. It is used during rollback,
		**   and to determine whether or not pages need to be journalled before
		**   being modified.
		**
		**   Throughout a write-transaction, dbFileSize contains the size of
		**   the file on disk in pages. It is set to a copy of dbSize when the
		**   write-transaction is first opened, and updated when VFS calls are made
		**   to write or truncate the database file on disk.
		**
		**   The only reason the dbFileSize variable is required is to suppress
		**   unnecessary calls to xTruncate() after committing a transaction. If,
		**   when a transaction is committed, the dbFileSize variable indicates
		**   that the database file is larger than the database image (Pager.dbSize),
		**   pager_truncate() is called. The pager_truncate() call uses xFilesize()
		**   to measure the database file on disk, and then truncates it if required.
		**   dbFileSize is not used when rolling back a transaction. In this case
		**   pager_truncate() is called unconditionally (which means there may be
		**   a call to xFilesize() that is not strictly required). In either case,
		**   pager_truncate() may cause the file to become smaller or larger.
		**
		** dbHintSize
		**
		**   The dbHintSize variable is used to limit the number of calls made to
		**   the VFS xFileControl(FCNTL_SIZE_HINT) method.
		**
		**   dbHintSize is set to a copy of the dbSize variable when a
		**   write-transaction is opened (at the same time as dbFileSize and
		**   dbOrigSize). If the xFileControl(FCNTL_SIZE_HINT) method is called,
		**   dbHintSize is increased to the number of pages that correspond to the
		**   size-hint passed to the method call. See pager_write_pagelist() for
		**   details.
		**
		** errCode
		**
		**   The Pager.errCode variable is only ever used in PAGER_ERROR state. It
		**   is set to zero in all other states. In PAGER_ERROR state, Pager.errCode
		**   is always set to SQLITE_FULL, SQLITE_IOERR or one of the SQLITE_IOERR_XXX
		**   sub-codes.
		*/

		public class Pager
		{
			public sqlite3_vfs pVfs;           /* OS functions to use for IO */
			public bool exclusiveMode;         /* Boolean. True if locking_mode==EXCLUSIVE */
			public u8 journalMode;             /* One of the PAGER_JOURNALMODE_* values */
			public u8 useJournal;              /* Use a rollback journal on this file */
			public u8 noReadlock;              /* Do not bother to obtain readlocks */
			public bool noSync;                /* Do not sync the journal if true */
			public bool fullSync;              /* Do extra syncs of the journal for robustness */
			public u8 ckptSyncFlags;           /* SYNC_NORMAL or SYNC_FULL for checkpoint */
			public u8 syncFlags;               /* SYNC_NORMAL or SYNC_FULL otherwise */
			public bool tempFile;              /* zFilename is a temporary file */
			public bool readOnly;              /* True for a read-only database */
			public bool alwaysRollback;        /* Disable DontRollback() for all pages */
			public u8 memDb;                   /* True to inhibit all file I/O */
			/**************************************************************************
			** The following block contains those class members that change during
			** routine opertion.  Class members not in this block are either fixed
			** when the pager is first created or else only change when there is a
			** significant mode change (such as changing the page_size, locking_mode,
			** or the journal_mode).  From another view, these class members describe
			** the "state" of the pager, while other class members describe the
			** "configuration" of the pager.
			*/
			public u8 eState;                  /* Pager state (OPEN, READER, WRITER_LOCKED..) */
			public u8 eLock;                   /* Current lock held on database file */
			public bool changeCountDone;       /* Set after incrementing the change-counter */
			public int setMaster;              /* True if a m-j name has been written to jrnl */
			public u8 doNotSpill;              /* Do not spill the cache when non-zero */
			public u8 doNotSyncSpill;          /* Do not do a spill that requires jrnl sync */
			public u8 subjInMemory;            /* True to use in-memory sub-journals */
			public Pgno dbSize;                /* Number of pages in the database */
			public Pgno dbOrigSize;            /* dbSize before the current transaction */
			public Pgno dbFileSize;            /* Number of pages in the database file */
			public Pgno dbHintSize;            /* Value passed to FCNTL_SIZE_HINT call */
			public int errCode;                /* One of several kinds of errors */
			public int nRec;                   /* Pages journalled since last j-header written */
			public u32 cksumInit;              /* Quasi-random value added to every checksum */
			public u32 nSubRec;                /* Number of records written to sub-journal */
			public Bitvec pInJournal;          /* One bit for each page in the database file */
			public sqlite3_file fd;            /* File descriptor for database */
			public sqlite3_file jfd;           /* File descriptor for main journal */
			public sqlite3_file sjfd;          /* File descriptor for sub-journal */
			public i64 journalOff;             /* Current write offset in the journal file */
			public i64 journalHdr;             /* Byte offset to previous journal header */
			public sqlite3_backup pBackup;     /* Pointer to list of ongoing backup processes */
			public PagerSavepoint[] aSavepoint;/* Array of active savepoints */
			public int nSavepoint;             /* Number of elements in aSavepoint[] */
			public u8[] dbFileVers = new u8[16];/* Changes whenever database file changes */
			/*
			** End of the routinely-changing class members
			***************************************************************************/

			public u16 nExtra;                 /* Add this many bytes to each in-memory page */
			public i16 nReserve;               /* Number of unused bytes at end of each page */
			public u32 vfsFlags;               /* Flags for sqlite3_vfs.xOpen() */
			public u32 sectorSize;             /* Assumed sector size during rollback */
			public int pageSize;               /* Number of bytes in a page */
			public Pgno mxPgno;                /* Maximum allowed size of the database */
			public i64 journalSizeLimit;       /* Size limit for persistent journal files */
			public string zFilename;           /* Name of the database file */
			public string zJournal;            /* Name of the journal file */
			public dxBusyHandler xBusyHandler; /* Function to call when busy */
			public object pBusyHandlerArg;     /* Context argument for xBusyHandler */
#if SQLITE_TEST || DEBUG
			public int nHit, nMiss;              /* Cache hits and missing */
			public int nRead, nWrite;            /* Database pages read/written */
#else
public int nHit;
#endif
			public dxReiniter xReiniter; //(DbPage*,int);/* Call this routine when reloading pages */
#if SQLITE_HAS_CODEC

			//void *(*xCodec)(void*,void*,Pgno,int);
			public dxCodec xCodec;                 /* Routine for en/decoding data */

			//void (*xCodecSizeChng)(void*,int,int);
			public dxCodecSizeChng xCodecSizeChng; /* Notify of page size changes */

			//void (*xCodecFree)(void*);
			public dxCodecFree xCodecFree;         /* Destructor for the codec */

			public codec_ctx pCodec;               /* First argument to xCodec... methods */
#endif
			public byte[] pTmpSpace;               /* Pager.pageSize bytes of space for tmp use */
			public PCache pPCache;                 /* Pointer to page cache object */
#if !SQLITE_OMIT_WAL
public Wal pWal;                       /* Write-ahead log used by "journal_mode=wal" */
public string zWal;                    /* File name for write-ahead log */
#else
			public sqlite3_vfs pWal = null;             /* Having this dummy here makes C# easier */
#endif
		};

		/*
		** The following global variables hold counters used for
		** testing purposes only.  These variables do not exist in
		** a non-testing build.  These variables are not thread-safe.
		*/
#if SQLITE_TEST
#if !TCLSH
    static int sqlite3_pager_readdb_count = 0;    /* Number of full pages read from DB */
    static int sqlite3_pager_writedb_count = 0;   /* Number of full pages written to DB */
    static int sqlite3_pager_writej_count = 0;    /* Number of pages written to journal */
#else
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_pager_readdb_count = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_pager_readdb_count" );
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_pager_writedb_count = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_pager_writedb_count" );
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_pager_writej_count = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_pager_writej_count" );
#endif
    static void PAGER_INCR( ref int v )
    {
      v++;
    }
#else

		//# define PAGER_INCR(v)
		private static void PAGER_INCR(ref int v)
		{
		}

#endif

		/*
** Journal files begin with the following magic string.  The data
** was obtained from /dev/random.  It is used only as a sanity check.
**
** Since version 2.8.0, the journal format contains additional sanity
** checking information.  If the power fails while the journal is being
** written, semi-random garbage data might appear in the journal
** file after power is restored.  If an attempt is then made
** to roll the journal back, the database could be corrupted.  The additional
** sanity checking data is an attempt to discover the garbage in the
** journal and ignore it.
**
** The sanity checking information for the new journal format consists
** of a 32-bit checksum on each page of data.  The checksum covers both
** the page number and the pPager.pageSize bytes of data for the page.
** This cksum is initialized to a 32-bit random value that appears in the
** journal file right after the header.  The random initializer is important,
** because garbage data that appears at the end of a journal is likely
** data that was once in other files that have now been deleted.  If the
** garbage data came from an obsolete journal file, the checksums might
** be correct.  But by initializing the checksum to random value which
** is different for every journal, we minimize that risk.
*/

		private static byte[] aJournalMagic = new byte[] {
0xd9, 0xd5, 0x05, 0xf9, 0x20, 0xa1, 0x63, 0xd7,
};

		/*
		** The size of the of each page record in the journal is given by
		** the following macro.
		*/

		//#define JOURNAL_PG_SZ(pPager)  ((pPager.pageSize) + 8)
		private static int JOURNAL_PG_SZ(Pager pPager)
		{
			return (pPager.pageSize + 8);
		}

		/*
		** The journal header size for this pager. This is usually the same
		** size as a single disk sector. See also setSectorSize().
		*/

		//#define JOURNAL_HDR_SZ(pPager) (pPager.sectorSize)
		private static u32 JOURNAL_HDR_SZ(Pager pPager)
		{
			return (pPager.sectorSize);
		}

		/*
		** The macro MEMDB is true if we are dealing with an in-memory database.
		** We do this as a macro so that if the SQLITE_OMIT_MEMORYDB macro is set,
		** the value of MEMDB will be a constant and the compiler will optimize
		** out code that would never execute.
		*/
#if SQLITE_OMIT_MEMORYDB
//# define MEMDB 0
const int MEMDB = 0;
#else
		//# define MEMDB pPager.memDb
#endif

		/*
** The maximum legal page number is (2^31 - 1).
*/

		//#define PAGER_MAX_PGNO 2147483647
		private const int PAGER_MAX_PGNO = 2147483647;

		/*
		** The argument to this macro is a file descriptor (type sqlite3_file*).
		** Return 0 if it is not open, or non-zero (but not 1) if it is.
		**
		** This is so that expressions can be written as:
		**
		**   if( isOpen(pPager.jfd) ){ ...
		**
		** instead of
		**
		**   if( pPager.jfd->pMethods ){ ...
		*/

		//#define isOpen(pFd) ((pFd)->pMethods)
		private static bool isOpen(sqlite3_file pFd)
		{
			return pFd.pMethods != null;
		}

		/*
		** Return true if this pager uses a write-ahead log instead of the usual
		** rollback journal. Otherwise false.
		*/
#if !SQLITE_OMIT_WAL
static int pagerUseWal(Pager *pPager){
return (pPager->pWal!=0);
}
#else

		//# define pagerUseWal(x) 0
		private static bool pagerUseWal(Pager x)
		{
			return false;
		}

		//# define pagerRollbackWal(x) 0
		private static int pagerRollbackWal(Pager x)
		{
			return 0;
		}

		//# define pagerWalFrames(v,w,x,y,z) 0
		private static int pagerWalFrames(Pager v, PgHdr w, Pgno x, int y, int z)
		{
			return 0;
		}

		//# define pagerOpenWalIfPresent(z) SQLITE_OK
		private static int pagerOpenWalIfPresent(Pager z)
		{
			return SQLITE_OK;
		}

		//# define pagerBeginReadTransaction(z) SQLITE_OK
		private static int pagerBeginReadTransaction(Pager z)
		{
			return SQLITE_OK;
		}

#endif

#if NDEBUG
    /*
** Usage:
**
**   Debug.Assert( assert_pager_state(pPager) );
**
** This function runs many Debug.Asserts to try to find inconsistencies in
** the internal state of the Pager object.
*/
    static bool assert_pager_state( Pager p )
    {
      Pager pPager = p;

      /* State must be valid. */
      Debug.Assert( p.eState == PAGER_OPEN
      || p.eState == PAGER_READER
      || p.eState == PAGER_WRITER_LOCKED
      || p.eState == PAGER_WRITER_CACHEMOD
      || p.eState == PAGER_WRITER_DBMOD
      || p.eState == PAGER_WRITER_FINISHED
      || p.eState == PAGER_ERROR
      );

      /* Regardless of the current state, a temp-file connection always behaves
      ** as if it has an exclusive lock on the database file. It never updates
      ** the change-counter field, so the changeCountDone flag is always set.
      */
      Debug.Assert( p.tempFile == false || p.eLock == EXCLUSIVE_LOCK );
      Debug.Assert( p.tempFile == false || pPager.changeCountDone );

      /* If the useJournal flag is clear, the journal-mode must be "OFF".
      ** And if the journal-mode is "OFF", the journal file must not be open.
      */
      Debug.Assert( p.journalMode == PAGER_JOURNALMODE_OFF || p.useJournal != 0 );
      Debug.Assert( p.journalMode != PAGER_JOURNALMODE_OFF || !isOpen( p.jfd ) );

      /* Check that MEMDB implies noSync. And an in-memory journal. Since
      ** this means an in-memory pager performs no IO at all, it cannot encounter
      ** either SQLITE_IOERR or SQLITE_FULL during rollback or while finalizing
      ** a journal file. (although the in-memory journal implementation may
      ** return SQLITE_IOERR_NOMEM while the journal file is being written). It
      ** is therefore not possible for an in-memory pager to enter the ERROR
      ** state.
      */
      if (
#if SQLITE_OMIT_MEMORYDB
0!=MEMDB
#else
 0 != pPager.memDb
#endif
 )
      {
        Debug.Assert( p.noSync );
        Debug.Assert( p.journalMode == PAGER_JOURNALMODE_OFF
        || p.journalMode == PAGER_JOURNALMODE_MEMORY
        );
        Debug.Assert( p.eState != PAGER_ERROR && p.eState != PAGER_OPEN );
        Debug.Assert( pagerUseWal( p ) == false );
      }

      /* If changeCountDone is set, a RESERVED lock or greater must be held
      ** on the file.
      */
      Debug.Assert( pPager.changeCountDone == false || pPager.eLock >= RESERVED_LOCK );
      Debug.Assert( p.eLock != PENDING_LOCK );

      switch ( p.eState )
      {
        case PAGER_OPEN:
          Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
 0 == pPager.memDb
#endif
 );
          Debug.Assert( pPager.errCode == SQLITE_OK );
          Debug.Assert( sqlite3PcacheRefCount( pPager.pPCache ) == 0 || pPager.tempFile );
          break;

        case PAGER_READER:
          Debug.Assert( pPager.errCode == SQLITE_OK );
          Debug.Assert( p.eLock != UNKNOWN_LOCK );
          Debug.Assert( p.eLock >= SHARED_LOCK || p.noReadlock != 0 );
          break;

        case PAGER_WRITER_LOCKED:
          Debug.Assert( p.eLock != UNKNOWN_LOCK );
          Debug.Assert( pPager.errCode == SQLITE_OK );
          if ( !pagerUseWal( pPager ) )
          {
            Debug.Assert( p.eLock >= RESERVED_LOCK );
          }
          Debug.Assert( pPager.dbSize == pPager.dbOrigSize );
          Debug.Assert( pPager.dbOrigSize == pPager.dbFileSize );
          Debug.Assert( pPager.dbOrigSize == pPager.dbHintSize );
          Debug.Assert( pPager.setMaster == 0 );
          break;

        case PAGER_WRITER_CACHEMOD:
          Debug.Assert( p.eLock != UNKNOWN_LOCK );
          Debug.Assert( pPager.errCode == SQLITE_OK );
          if ( !pagerUseWal( pPager ) )
          {
            /* It is possible that if journal_mode=wal here that neither the
            ** journal file nor the WAL file are open. This happens during
            ** a rollback transaction that switches from journal_mode=off
            ** to journal_mode=wal.
            */
            Debug.Assert( p.eLock >= RESERVED_LOCK );
            Debug.Assert( isOpen( p.jfd )
            || p.journalMode == PAGER_JOURNALMODE_OFF
            || p.journalMode == PAGER_JOURNALMODE_WAL
            );
          }
          Debug.Assert( pPager.dbOrigSize == pPager.dbFileSize );
          Debug.Assert( pPager.dbOrigSize == pPager.dbHintSize );
          break;

        case PAGER_WRITER_DBMOD:
          Debug.Assert( p.eLock == EXCLUSIVE_LOCK );
          Debug.Assert( pPager.errCode == SQLITE_OK );
          Debug.Assert( !pagerUseWal( pPager ) );
          Debug.Assert( p.eLock >= EXCLUSIVE_LOCK );
          Debug.Assert( isOpen( p.jfd )
          || p.journalMode == PAGER_JOURNALMODE_OFF
          || p.journalMode == PAGER_JOURNALMODE_WAL
          );
          Debug.Assert( pPager.dbOrigSize <= pPager.dbHintSize );
          break;

        case PAGER_WRITER_FINISHED:
          Debug.Assert( p.eLock == EXCLUSIVE_LOCK );
          Debug.Assert( pPager.errCode == SQLITE_OK );
          Debug.Assert( !pagerUseWal( pPager ) );
          Debug.Assert( isOpen( p.jfd )
          || p.journalMode == PAGER_JOURNALMODE_OFF
          || p.journalMode == PAGER_JOURNALMODE_WAL
          );
          break;

        case PAGER_ERROR:
          /* There must be at least one outstanding reference to the pager if
          ** in ERROR state. Otherwise the pager should have already dropped
          ** back to OPEN state.
          */
          Debug.Assert( pPager.errCode != SQLITE_OK );
          Debug.Assert( sqlite3PcacheRefCount( pPager.pPCache ) > 0 );
          break;
      }

      return true;
    }
#else

		private static bool assert_pager_state(Pager pPager)
		{
			return true;
		}

#endif //* ifndef NDEBUG */

#if SQLITE_DEBUG
		/*
** Return a pointer to a human readable string in a static buffer
** containing the state of the Pager object passed as an argument. This
** is intended to be used within debuggers. For example, as an alternative
** to "print *pPager" in gdb:
**
** (gdb) printf "%s", print_pager_state(pPager)
*/

		private static string print_pager_state(Pager p)
		{
			StringBuilder zRet = new StringBuilder(1024);

			sqlite3_snprintf(1024, zRet,
			"Filename:      %s\n" +
			"State:         %s errCode=%d\n" +
			"Lock:          %s\n" +
			"Locking mode:  locking_mode=%s\n" +
			"Journal mode:  journal_mode=%s\n" +
			"Backing store: tempFile=%d memDb=%d useJournal=%d\n" +
			"Journal:       journalOff=%lld journalHdr=%lld\n" +
			"Size:          dbsize=%d dbOrigSize=%d dbFileSize=%d\n"
			, p.zFilename
			, p.eState == PAGER_OPEN ? "OPEN" :
			p.eState == PAGER_READER ? "READER" :
			p.eState == PAGER_WRITER_LOCKED ? "WRITER_LOCKED" :
			p.eState == PAGER_WRITER_CACHEMOD ? "WRITER_CACHEMOD" :
			p.eState == PAGER_WRITER_DBMOD ? "WRITER_DBMOD" :
			p.eState == PAGER_WRITER_FINISHED ? "WRITER_FINISHED" :
			p.eState == PAGER_ERROR ? "ERROR" : "?error?"
			, (int)p.errCode
			, p.eLock == NO_LOCK ? "NO_LOCK" :
			p.eLock == RESERVED_LOCK ? "RESERVED" :
			p.eLock == EXCLUSIVE_LOCK ? "EXCLUSIVE" :
			p.eLock == SHARED_LOCK ? "SHARED" :
			p.eLock == UNKNOWN_LOCK ? "UNKNOWN" : "?error?"
			, p.exclusiveMode ? "exclusive" : "normal"
			, p.journalMode == PAGER_JOURNALMODE_MEMORY ? "memory" :
			p.journalMode == PAGER_JOURNALMODE_OFF ? "off" :
			p.journalMode == PAGER_JOURNALMODE_DELETE ? "delete" :
			p.journalMode == PAGER_JOURNALMODE_PERSIST ? "persist" :
			p.journalMode == PAGER_JOURNALMODE_TRUNCATE ? "truncate" :
			p.journalMode == PAGER_JOURNALMODE_WAL ? "wal" : "?error?"
			, p.tempFile ? 1 : 0, (int)p.memDb, (int)p.useJournal
			, p.journalOff, p.journalHdr
			, (int)p.dbSize, (int)p.dbOrigSize, (int)p.dbFileSize
			);

			return zRet.ToString();
		}

#endif

		/*
** Return true if it is necessary to write page *pPg into the sub-journal.
** A page needs to be written into the sub-journal if there exists one
** or more open savepoints for which:
**
**   * The page-number is less than or equal to PagerSavepoint.nOrig, and
**   * The bit corresponding to the page-number is not set in
**     PagerSavepoint.pInSavepoint.
*/

		private static bool subjRequiresPage(PgHdr pPg)
		{
			u32 pgno = pPg.pgno;
			Pager pPager = pPg.pPager;
			int i;
			for (i = 0; i < pPager.nSavepoint; i++)
			{
				PagerSavepoint p = pPager.aSavepoint[i];
				if (p.nOrig >= pgno && 0 == sqlite3BitvecTest(p.pInSavepoint, pgno))
				{
					return true;
				}
			}
			return false;
		}

		/*
		** Return true if the page is already in the journal file.
		*/

		private static bool pageInJournal(PgHdr pPg)
		{
			return sqlite3BitvecTest(pPg.pPager.pInJournal, pPg.pgno) != 0;
		}

		/*
		** Read a 32-bit integer from the given file descriptor.  Store the integer
		** that is read in pRes.  Return SQLITE_OK if everything worked, or an
		** error code is something goes wrong.
		**
		** All values are stored on disk as big-endian.
		*/

		private static int read32bits(sqlite3_file fd, int offset, ref int pRes)
		{
			u32 u32_pRes = 0;
			int rc = read32bits(fd, offset, ref u32_pRes);
			pRes = (int)u32_pRes;
			return rc;
		}

		private static int read32bits(sqlite3_file fd, i64 offset, ref u32 pRes)
		{
			int rc = read32bits(fd, (int)offset, ref pRes);
			return rc;
		}

		private static int read32bits(sqlite3_file fd, int offset, ref u32 pRes)
		{
			byte[] ac = new byte[4];
			int rc = sqlite3OsRead(fd, ac, ac.Length, offset);
			if (rc == SQLITE_OK)
			{
				pRes = sqlite3Get4byte(ac);
			}
			else
				pRes = 0;
			return rc;
		}

		/*
		** Write a 32-bit integer into a string buffer in big-endian byte order.
		*/

		//#define put32bits(A,B)  sqlite3sqlite3Put4byte((u8*)A,B)
		private static void put32bits(string ac, int offset, int val)
		{
			byte[] A = new byte[4];
			A[0] = (byte)ac[offset + 0];
			A[1] = (byte)ac[offset + 1];
			A[2] = (byte)ac[offset + 2];
			A[3] = (byte)ac[offset + 3];
			sqlite3Put4byte(A, 0, val);
		}

		private static void put32bits(byte[] ac, int offset, int val)
		{
			sqlite3Put4byte(ac, offset, (u32)val);
		}

		private static void put32bits(byte[] ac, u32 val)
		{
			sqlite3Put4byte(ac, 0U, val);
		}

		private static void put32bits(byte[] ac, int offset, u32 val)
		{
			sqlite3Put4byte(ac, offset, val);
		}

		/*
		** Write a 32-bit integer into the given file descriptor.  Return SQLITE_OK
		** on success or an error code is something goes wrong.
		*/

		private static int write32bits(sqlite3_file fd, i64 offset, u32 val)
		{
			byte[] ac = new byte[4];
			put32bits(ac, val);
			return sqlite3OsWrite(fd, ac, 4, offset);
		}

		/*
		** Unlock the database file to level eLock, which must be either NO_LOCK
		** or SHARED_LOCK. Regardless of whether or not the call to xUnlock()
		** succeeds, set the Pager.eLock variable to match the (attempted) new lock.
		**
		** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is
		** called, do not modify it. See the comment above the #define of
		** UNKNOWN_LOCK for an explanation of this.
		*/

		private static int pagerUnlockDb(Pager pPager, int eLock)
		{
			int rc = SQLITE_OK;

			Debug.Assert(!pPager.exclusiveMode || pPager.eLock == eLock);
			Debug.Assert(eLock == NO_LOCK || eLock == SHARED_LOCK);
			Debug.Assert(eLock != NO_LOCK || pagerUseWal(pPager) == false);
			if (isOpen(pPager.fd))
			{
				Debug.Assert(pPager.eLock >= eLock);
				rc = sqlite3OsUnlock(pPager.fd, eLock);
				if (pPager.eLock != UNKNOWN_LOCK)
				{
					pPager.eLock = (u8)eLock;
				}
				IOTRACE("UNLOCK %p %d\n", pPager, eLock);
			}
			return rc;
		}

		/*
		** Lock the database file to level eLock, which must be either SHARED_LOCK,
		** RESERVED_LOCK or EXCLUSIVE_LOCK. If the caller is successful, set the
		** Pager.eLock variable to the new locking state.
		**
		** Except, if Pager.eLock is set to UNKNOWN_LOCK when this function is
		** called, do not modify it unless the new locking state is EXCLUSIVE_LOCK.
		** See the comment above the #define of UNKNOWN_LOCK for an explanation
		** of this.
		*/

		private static int pagerLockDb(Pager pPager, int eLock)
		{
			int rc = SQLITE_OK;

			Debug.Assert(eLock == SHARED_LOCK || eLock == RESERVED_LOCK || eLock == EXCLUSIVE_LOCK);
			if (pPager.eLock < eLock || pPager.eLock == UNKNOWN_LOCK)
			{
				rc = sqlite3OsLock(pPager.fd, eLock);
				if (rc == SQLITE_OK && (pPager.eLock != UNKNOWN_LOCK || eLock == EXCLUSIVE_LOCK))
				{
					pPager.eLock = (u8)eLock;
					IOTRACE("LOCK %p %d\n", pPager, eLock);
				}
			}
			return rc;
		}

		/*
		** This function determines whether or not the atomic-write optimization
		** can be used with this pager. The optimization can be used if:
		**
		**  (a) the value returned by OsDeviceCharacteristics() indicates that
		**      a database page may be written atomically, and
		**  (b) the value returned by OsSectorSize() is less than or equal
		**      to the page size.
		**
		** The optimization is also always enabled for temporary files. It is
		** an error to call this function if pPager is opened on an in-memory
		** database.
		**
		** If the optimization cannot be used, 0 is returned. If it can be used,
		** then the value returned is the size of the journal file when it
		** contains rollback data for exactly one page.
		*/
#if SQLITE_ENABLE_ATOMIC_WRITE
static int jrnlBufferSize(Pager *pPager){
Debug.Assert( 0==MEMDB );
if( !pPager.tempFile ){
int dc;                           /* Device characteristics */
int nSector;                      /* Sector size */
int szPage;                       /* Page size */

Debug.Assert( isOpen(pPager.fd) );
dc = sqlite3OsDeviceCharacteristics(pPager.fd);
nSector = pPager.sectorSize;
szPage = pPager.pageSize;

Debug.Assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
Debug.Assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
if( 0==(dc&(SQLITE_IOCAP_ATOMIC|(szPage>>8)) || nSector>szPage) ){
return 0;
}
}

return JOURNAL_HDR_SZ(pPager) + JOURNAL_PG_SZ(pPager);
}
#endif

		/*
** If SQLITE_CHECK_PAGES is defined then we do some sanity checking
** on the cache using a hash function.  This is used for testing
** and debugging only.
*/
#if SQLITE_CHECK_PAGES
/*
** Return a 32-bit hash of the page data for pPage.
*/
static u32 pager_datahash(int nByte, unsigned char pData){
u32 hash = 0;
int i;
for(i=0; i<nByte; i++){
hash = (hash*1039) + pData[i];
}
return hash;
}
static void pager_pagehash(PgHdr pPage){
return pager_datahash(pPage.pPager.pageSize, (unsigned char *)pPage.pData);
}
static u32 pager_set_pagehash(PgHdr pPage){
pPage.pageHash = pager_pagehash(pPage);
}

/*
** The CHECK_PAGE macro takes a PgHdr* as an argument. If SQLITE_CHECK_PAGES
** is defined, and NDEBUG is not defined, an Debug.Assert() statement checks
** that the page is either dirty or still matches the calculated page-hash.
*/
//#define CHECK_PAGE(x) checkPage(x)
static void checkPage(PgHdr pPg){
Pager pPager = pPg.pPager;
assert( pPager->eState!=PAGER_ERROR );
assert( (pPg->flags&PGHDR_DIRTY) || pPg->pageHash==pager_pagehash(pPg) );
}

#else

		//#define pager_datahash(X,Y)  0
		private static int pager_datahash(int X, byte[] Y)
		{
			return 0;
		}

		//#define pager_pagehash(X)  0
		private static int pager_pagehash(PgHdr X)
		{
			return 0;
		}

		//#define pager_set_pagehash(X)
		private static void pager_set_pagehash(PgHdr X)
		{
		}

		//#define CHECK_PAGE(x)
#endif //* SQLITE_CHECK_PAGES */

		/*
** When this is called the journal file for pager pPager must be open.
** This function attempts to read a master journal file name from the
** end of the file and, if successful, copies it into memory supplied
** by the caller. See comments above writeMasterJournal() for the format
** used to store a master journal file name at the end of a journal file.
**
** zMaster must point to a buffer of at least nMaster bytes allocated by
** the caller. This should be sqlite3_vfs.mxPathname+1 (to ensure there is
** enough space to write the master journal name). If the master journal
** name in the journal is longer than nMaster bytes (including a
** nul-terminator), then this is handled as if no master journal name
** were present in the journal.
**
** If a master journal file name is present at the end of the journal
** file, then it is copied into the buffer pointed to by zMaster. A
** nul-terminator byte is appended to the buffer following the master
** journal file name.
**
** If it is determined that no master journal file name is present
** zMaster[0] is set to 0 and SQLITE_OK returned.
**
** If an error occurs while reading from the journal file, an SQLite
** error code is returned.
*/

		private static int readMasterJournal(sqlite3_file pJrnl, byte[] zMaster, u32 nMaster)
		{
			int rc;                       /* Return code */
			int len = 0;                  /* Length in bytes of master journal name */
			i64 szJ = 0;                 /* Total size in bytes of journal file pJrnl */
			u32 cksum = 0;                /* MJ checksum value read from journal */
			int u;                        /* Unsigned loop counter */
			byte[] aMagic = new byte[8];  /* A buffer to hold the magic header */

			zMaster[0] = 0;

			if (SQLITE_OK != (rc = sqlite3OsFileSize(pJrnl, ref szJ))
			|| szJ < 16
			|| SQLITE_OK != (rc = read32bits(pJrnl, (int)(szJ - 16), ref len))
			|| len >= nMaster
			|| SQLITE_OK != (rc = read32bits(pJrnl, szJ - 12, ref cksum))
			|| SQLITE_OK != (rc = sqlite3OsRead(pJrnl, aMagic, 8, szJ - 8))
			|| memcmp(aMagic, aJournalMagic, 8) != 0
			|| SQLITE_OK != (rc = sqlite3OsRead(pJrnl, zMaster, len, (long)(szJ - 16 - len)))
			)
			{
				return rc;
			}

			/* See if the checksum matches the master journal name */
			for (u = 0; u < len; u++)
			{
				cksum -= zMaster[u];
			}
			if (cksum != 0)
			{
				/* If the checksum doesn't add up, then one or more of the disk sectors
				** containing the master journal filename is corrupted. This means
				** definitely roll back, so just return SQLITE_OK and report a (nul)
				** master-journal filename.
				*/
				len = 0;
			}
			if (len == 0)
				zMaster[0] = 0;

			return SQLITE_OK;
		}

		/*
		** Return the offset of the sector boundary at or immediately
		** following the value in pPager.journalOff, assuming a sector
		** size of pPager.sectorSize bytes.
		**
		** i.e for a sector size of 512:
		**
		**   Pager.journalOff          Return value
		**   ---------------------------------------
		**   0                         0
		**   512                       512
		**   100                       512
		**   2000                      2048
		**
		*/

		private static i64 journalHdrOffset(Pager pPager)
		{
			i64 offset = 0;
			i64 c = pPager.journalOff;
			if (c != 0)
			{
				offset = (int)(((c - 1) / pPager.sectorSize + 1) * pPager.sectorSize);//offset = ((c-1)/JOURNAL_HDR_SZ(pPager) + 1) * JOURNAL_HDR_SZ(pPager);
			}
			Debug.Assert(offset % pPager.sectorSize == 0); //Debug.Assert(offset % JOURNAL_HDR_SZ(pPager) == 0);
			Debug.Assert(offset >= c);
			Debug.Assert((offset - c) < pPager.sectorSize);//Debug.Assert( (offset-c)<JOURNAL_HDR_SZ(pPager) );
			return offset;
		}

		private static void seekJournalHdr(Pager pPager)
		{
			pPager.journalOff = journalHdrOffset(pPager);
		}

		/*
		** The journal file must be open when this function is called.
		**
		** This function is a no-op if the journal file has not been written to
		** within the current transaction (i.e. if Pager.journalOff==0).
		**
		** If doTruncate is non-zero or the Pager.journalSizeLimit variable is
		** set to 0, then truncate the journal file to zero bytes in size. Otherwise,
		** zero the 28-byte header at the start of the journal file. In either case,
		** if the pager is not in no-sync mode, sync the journal file immediately
		** after writing or truncating it.
		**
		** If Pager.journalSizeLimit is set to a positive, non-zero value, and
		** following the truncation or zeroing described above the size of the
		** journal file in bytes is larger than this value, then truncate the
		** journal file to Pager.journalSizeLimit bytes. The journal file does
		** not need to be synced following this operation.
		**
		** If an IO error occurs, abandon processing and return the IO error code.
		** Otherwise, return SQLITE_OK.
		*/

		private static int zeroJournalHdr(Pager pPager, int doTruncate)
		{
			int rc = SQLITE_OK;                               /* Return code */
			Debug.Assert(isOpen(pPager.jfd));

			if (pPager.journalOff != 0)
			{
				i64 iLimit = pPager.journalSizeLimit;           /* Local cache of jsl */
				IOTRACE("JZEROHDR %p\n", pPager);
				if (doTruncate != 0 || iLimit == 0)
				{
					rc = sqlite3OsTruncate(pPager.jfd, 0);
				}
				else
				{
					byte[] zeroHdr = new byte[28];// = {0};
					rc = sqlite3OsWrite(pPager.jfd, zeroHdr, zeroHdr.Length, 0);
				}
				if (rc == SQLITE_OK && !pPager.noSync)
				{
					rc = sqlite3OsSync(pPager.jfd, SQLITE_SYNC_DATAONLY | pPager.syncFlags);
				}

				/* At this point the transaction is committed but the write lock
				** is still held on the file. If there is a size limit configured for
				** the persistent journal and the journal file currently consumes more
				** space than that limit allows for, truncate it now. There is no need
				** to sync the file following this operation.
				*/
				if (rc == SQLITE_OK && iLimit > 0)
				{
					i64 sz = 0;
					rc = sqlite3OsFileSize(pPager.jfd, ref sz);
					if (rc == SQLITE_OK && sz > iLimit)
					{
						rc = sqlite3OsTruncate(pPager.jfd, iLimit);
					}
				}
			}
			return rc;
		}

		/*
		** The journal file must be open when this routine is called. A journal
		** header (JOURNAL_HDR_SZ bytes) is written into the journal file at the
		** current location.
		**
		** The format for the journal header is as follows:
		** - 8 bytes: Magic identifying journal format.
		** - 4 bytes: Number of records in journal, or -1 no-sync mode is on.
		** - 4 bytes: Random number used for page hash.
		** - 4 bytes: Initial database page count.
		** - 4 bytes: Sector size used by the process that wrote this journal.
		** - 4 bytes: Database page size.
		**
		** Followed by (JOURNAL_HDR_SZ - 28) bytes of unused space.
		*/

		private static int writeJournalHdr(Pager pPager)
		{
			int rc = SQLITE_OK;                 /* Return code */
			byte[] zHeader = pPager.pTmpSpace;  /* Temporary space used to build header */
			u32 nHeader = (u32)pPager.pageSize; /* Size of buffer pointed to by zHeader */
			u32 nWrite;                         /* Bytes of header sector written */
			int ii;                             /* Loop counter */

			Debug.Assert(isOpen(pPager.jfd));      /* Journal file must be open. */

			if (nHeader > JOURNAL_HDR_SZ(pPager))
			{
				nHeader = JOURNAL_HDR_SZ(pPager);
			}
			/* If there are active savepoints and any of them were created
			** since the most recent journal header was written, update the
			** PagerSavepoint.iHdrOffset fields now.
			*/
			for (ii = 0; ii < pPager.nSavepoint; ii++)
			{
				if (pPager.aSavepoint[ii].iHdrOffset == 0)
				{
					pPager.aSavepoint[ii].iHdrOffset = pPager.journalOff;
				}
			}
			pPager.journalHdr = pPager.journalOff = journalHdrOffset(pPager);

			/*
			** Write the nRec Field - the number of page records that follow this
			** journal header. Normally, zero is written to this value at this time.
			** After the records are added to the journal (and the journal synced,
			** if in full-sync mode), the zero is overwritten with the true number
			** of records (see syncJournal()).
			**
			** A faster alternative is to write 0xFFFFFFFF to the nRec field. When
			** reading the journal this value tells SQLite to assume that the
			** rest of the journal file contains valid page records. This assumption
			** is dangerous, as if a failure occurred whilst writing to the journal
			** file it may contain some garbage data. There are two scenarios
			** where this risk can be ignored:
			**
			**   * When the pager is in no-sync mode. Corruption can follow a
			**     power failure in this case anyway.
			**
			**   * When the SQLITE_IOCAP_SAFE_APPEND flag is set. This guarantees
			**     that garbage data is never appended to the journal file.
			*/
			Debug.Assert(isOpen(pPager.fd) || pPager.noSync);
			if (pPager.noSync || (pPager.journalMode == PAGER_JOURNALMODE_MEMORY)
			|| (sqlite3OsDeviceCharacteristics(pPager.fd) & SQLITE_IOCAP_SAFE_APPEND) != 0
			)
			{
				aJournalMagic.CopyTo(zHeader, 0);// memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
				put32bits(zHeader, aJournalMagic.Length, 0xffffffff);
			}
			else
			{
				Array.Clear(zHeader, 0, aJournalMagic.Length + 4);//memset(zHeader, 0, sizeof(aJournalMagic)+4);
			}

			/* The random check-hash initialiser */
			i64 i64Temp = 0;
			sqlite3_randomness(sizeof(i64), ref i64Temp);
			pPager.cksumInit = (u32)i64Temp;
			put32bits(zHeader, aJournalMagic.Length + 4, pPager.cksumInit);
			/* The initial database size */
			put32bits(zHeader, aJournalMagic.Length + 8, pPager.dbOrigSize);
			/* The assumed sector size for this process */
			put32bits(zHeader, aJournalMagic.Length + 12, pPager.sectorSize);
			/* The page size */
			put32bits(zHeader, aJournalMagic.Length + 16, (u32)pPager.pageSize);

			/* Initializing the tail of the buffer is not necessary.  Everything
			** works find if the following memset() is omitted.  But initializing
			** the memory prevents valgrind from complaining, so we are willing to
			** take the performance hit.
			*/
			//  memset(&zHeader[sizeof(aJournalMagic)+20], 0,
			//  nHeader-(sizeof(aJournalMagic)+20));
			Array.Clear(zHeader, aJournalMagic.Length + 20, (int)nHeader - (aJournalMagic.Length + 20));

			/* In theory, it is only necessary to write the 28 bytes that the
			** journal header consumes to the journal file here. Then increment the
			** Pager.journalOff variable by JOURNAL_HDR_SZ so that the next
			** record is written to the following sector (leaving a gap in the file
			** that will be implicitly filled in by the OS).
			**
			** However it has been discovered that on some systems this pattern can
			** be significantly slower than contiguously writing data to the file,
			** even if that means explicitly writing data to the block of
			** (JOURNAL_HDR_SZ - 28) bytes that will not be used. So that is what
			** is done.
			**
			** The loop is required here in case the sector-size is larger than the
			** database page size. Since the zHeader buffer is only Pager.pageSize
			** bytes in size, more than one call to sqlite3OsWrite() may be required
			** to populate the entire journal header sector.
			*/
			for (nWrite = 0; rc == SQLITE_OK && nWrite < JOURNAL_HDR_SZ(pPager); nWrite += nHeader)
			{
				IOTRACE("JHDR %p %lld %d\n", pPager, pPager.journalHdr, nHeader);
				rc = sqlite3OsWrite(pPager.jfd, zHeader, (int)nHeader, pPager.journalOff);
				Debug.Assert(pPager.journalHdr <= pPager.journalOff);
				pPager.journalOff += (int)nHeader;
			}
			return rc;
		}

		/*
		** The journal file must be open when this is called. A journal header file
		** (JOURNAL_HDR_SZ bytes) is read from the current location in the journal
		** file. The current location in the journal file is given by
		** pPager.journalOff. See comments above function writeJournalHdr() for
		** a description of the journal header format.
		**
		** If the header is read successfully, *pNRec is set to the number of
		** page records following this header and *pDbSize is set to the size of the
		** database before the transaction began, in pages. Also, pPager.cksumInit
		** is set to the value read from the journal header. SQLITE_OK is returned
		** in this case.
		**
		** If the journal header file appears to be corrupted, SQLITE_DONE is
		** returned and *pNRec and *PDbSize are undefined.  If JOURNAL_HDR_SZ bytes
		** cannot be read from the journal file an error code is returned.
		*/

		private static int readJournalHdr(
		Pager pPager,               /* Pager object */
		int isHot,
		i64 journalSize,            /* Size of the open journal file in bytes */
		out u32 pNRec,              /* OUT: Value read from the nRec field */
		out u32 pDbSize             /* OUT: Value of original database size field */
		)
		{
			int rc;                      /* Return code */
			byte[] aMagic = new byte[8]; /* A buffer to hold the magic header */
			i64 iHdrOff;                 /* Offset of journal header being read */

			Debug.Assert(isOpen(pPager.jfd));      /* Journal file must be open. */

			pNRec = 0;
			pDbSize = 0;

			/* Advance Pager.journalOff to the start of the next sector. If the
			** journal file is too small for there to be a header stored at this
			** point, return SQLITE_DONE.
			*/
			pPager.journalOff = journalHdrOffset(pPager);
			if (pPager.journalOff + JOURNAL_HDR_SZ(pPager) > journalSize)
			{
				return SQLITE_DONE;
			}
			iHdrOff = pPager.journalOff;

			/* Read in the first 8 bytes of the journal header. If they do not match
			** the  magic string found at the start of each journal header, return
			** SQLITE_DONE. If an IO error occurs, return an error code. Otherwise,
			** proceed.
			*/
			if (isHot != 0 || iHdrOff != pPager.journalHdr)
			{
				rc = sqlite3OsRead(pPager.jfd, aMagic, aMagic.Length, iHdrOff);
				if (rc != 0)
				{
					return rc;
				}
				if (memcmp(aMagic, aJournalMagic, aMagic.Length) != 0)
				{
					return SQLITE_DONE;
				}
			}
			/* Read the first three 32-bit fields of the journal header: The nRec
			** field, the checksum-initializer and the database size at the start
			** of the transaction. Return an error code if anything goes wrong.
			*/
			if (SQLITE_OK != (rc = read32bits(pPager.jfd, iHdrOff + 8, ref pNRec))
			|| SQLITE_OK != (rc = read32bits(pPager.jfd, iHdrOff + 12, ref pPager.cksumInit))
			|| SQLITE_OK != (rc = read32bits(pPager.jfd, iHdrOff + 16, ref pDbSize))
			)
			{
				return rc;
			}

			if (pPager.journalOff == 0)
			{
				u32 iPageSize = 0;           /* Page-size field of journal header */
				u32 iSectorSize = 0;         /* Sector-size field of journal header */

				/* Read the page-size and sector-size journal header fields. */
				if (SQLITE_OK != (rc = read32bits(pPager.jfd, iHdrOff + 20, ref iSectorSize))
				|| SQLITE_OK != (rc = read32bits(pPager.jfd, iHdrOff + 24, ref iPageSize))
				)
				{
					return rc;
				}

				/* Versions of SQLite prior to 3.5.8 set the page-size field of the
				** journal header to zero. In this case, assume that the Pager.pageSize
				** variable is already set to the correct page size.
				*/
				if (iPageSize == 0)
				{
					iPageSize = (u32)pPager.pageSize;
				}

				/* Check that the values read from the page-size and sector-size fields
				** are within range. To be 'in range', both values need to be a power
				** of two greater than or equal to 512 or 32, and not greater than their
				** respective compile time maximum limits.
				*/
				if (iPageSize < 512 || iSectorSize < 32
				|| iPageSize > SQLITE_MAX_PAGE_SIZE || iSectorSize > MAX_SECTOR_SIZE
				|| ((iPageSize - 1) & iPageSize) != 0 || ((iSectorSize - 1) & iSectorSize) != 0
				)
				{
					/* If the either the page-size or sector-size in the journal-header is
					** invalid, then the process that wrote the journal-header must have
					** crashed before the header was synced. In this case stop reading
					** the journal file here.
					*/
					return SQLITE_DONE;
				}

				/* Update the page-size to match the value read from the journal.
				** Use a testcase() macro to make sure that malloc failure within
				** PagerSetPagesize() is tested.
				*/
				rc = sqlite3PagerSetPagesize(pPager, ref iPageSize, -1);
				testcase(rc != SQLITE_OK);

				/* Update the assumed sector-size to match the value used by
				** the process that created this journal. If this journal was
				** created by a process other than this one, then this routine
				** is being called from within pager_playback(). The local value
				** of Pager.sectorSize is restored at the end of that routine.
				*/
				pPager.sectorSize = iSectorSize;
			}

			pPager.journalOff += (int)JOURNAL_HDR_SZ(pPager);
			return rc;
		}

		/*
		** Write the supplied master journal name into the journal file for pager
		** pPager at the current location. The master journal name must be the last
		** thing written to a journal file. If the pager is in full-sync mode, the
		** journal file descriptor is advanced to the next sector boundary before
		** anything is written. The format is:
		**
		**   + 4 bytes: PAGER_MJ_PGNO.
		**   + N bytes: Master journal filename in utf-8.
		**   + 4 bytes: N (length of master journal name in bytes, no nul-terminator).
		**   + 4 bytes: Master journal name checksum.
		**   + 8 bytes: aJournalMagic[].
		**
		** The master journal page checksum is the sum of the bytes in the master
		** journal name, where each byte is interpreted as a signed 8-bit integer.
		**
		** If zMaster is a NULL pointer (occurs for a single database transaction),
		** this call is a no-op.
		*/

		private static int writeMasterJournal(Pager pPager, string zMaster)
		{
			int rc;                          /* Return code */
			int nMaster;                     /* Length of string zMaster */
			i64 iHdrOff;                     /* Offset of header in journal file */
			i64 jrnlSize = 0;                  /* Size of journal file on disk */
			u32 cksum = 0;                   /* Checksum of string zMaster */

			Debug.Assert(pPager.setMaster == 0);
			Debug.Assert(!pagerUseWal(pPager));
			if (null == zMaster
			|| pPager.journalMode == PAGER_JOURNALMODE_MEMORY
			|| pPager.journalMode == PAGER_JOURNALMODE_OFF
			)
			{
				return SQLITE_OK;
			}

			pPager.setMaster = 1;
			Debug.Assert(isOpen(pPager.jfd));
			Debug.Assert(pPager.journalHdr <= pPager.journalOff);

			/* Calculate the length in bytes and the checksum of zMaster */
			for (nMaster = 0; nMaster < zMaster.Length && zMaster[nMaster] != 0; nMaster++)
			{
				cksum += zMaster[nMaster];
			}

			/* If in full-sync mode, advance to the next disk sector before writing
			** the master journal name. This is in case the previous page written to
			** the journal has already been synced.
			*/
			if (pPager.fullSync)
			{
				pPager.journalOff = journalHdrOffset(pPager);
			}
			iHdrOff = pPager.journalOff;
			/* Write the master journal data to the end of the journal file. If
			** an error occurs, return the error code to the caller.
			*/
			if ((0 != (rc = write32bits(pPager.jfd, iHdrOff, (u32)PAGER_MJ_PGNO(pPager))))
			|| (0 != (rc = sqlite3OsWrite(pPager.jfd, Encoding.UTF8.GetBytes(zMaster), nMaster, iHdrOff + 4)))
			|| (0 != (rc = write32bits(pPager.jfd, iHdrOff + 4 + nMaster, (u32)nMaster)))
			|| (0 != (rc = write32bits(pPager.jfd, iHdrOff + 4 + nMaster + 4, cksum)))
			|| (0 != (rc = sqlite3OsWrite(pPager.jfd, aJournalMagic, 8, iHdrOff + 4 + nMaster + 8)))
			)
			{
				return rc;
			}
			pPager.journalOff += (nMaster + 20);

			/* If the pager is in peristent-journal mode, then the physical
			** journal-file may extend past the end of the master-journal name
			** and 8 bytes of magic data just written to the file. This is
			** dangerous because the code to rollback a hot-journal file
			** will not be able to find the master-journal name to determine
			** whether or not the journal is hot.
			**
			** Easiest thing to do in this scenario is to truncate the journal
			** file to the required size.
			*/
			if (SQLITE_OK == (rc = sqlite3OsFileSize(pPager.jfd, ref jrnlSize))
			&& jrnlSize > pPager.journalOff
			)
			{
				rc = sqlite3OsTruncate(pPager.jfd, pPager.journalOff);
			}

			return rc;
		}

		/*
		** Find a page in the hash table given its page number. Return
		** a pointer to the page or NULL if the requested page is not
		** already in memory.
		*/

		private static PgHdr pager_lookup(Pager pPager, u32 pgno)
		{
			PgHdr p = null;                         /* Return value */
			/* It is not possible for a call to PcacheFetch() with createFlag==0 to
			** fail, since no attempt to allocate dynamic memory will be made.
			*/
			sqlite3PcacheFetch(pPager.pPCache, pgno, 0, ref p);
			return p;
		}

		/*
		** Discard the entire contents of the in-memory page-cache.
		*/

		private static void pager_reset(Pager pPager)
		{
			sqlite3BackupRestart(pPager.pBackup);
			sqlite3PcacheClear(pPager.pPCache);
		}

		/*
		** Free all structures in the Pager.aSavepoint[] array and set both
		** Pager.aSavepoint and Pager.nSavepoint to zero. Close the sub-journal
		** if it is open and the pager is not in exclusive mode.
		*/

		private static void releaseAllSavepoints(Pager pPager)
		{
			int ii;               /* Iterator for looping through Pager.aSavepoint */
			for (ii = 0; ii < pPager.nSavepoint; ii++)
			{
				sqlite3BitvecDestroy(ref pPager.aSavepoint[ii].pInSavepoint);
			}
			if (!pPager.exclusiveMode || sqlite3IsMemJournal(pPager.sjfd))
			{
				sqlite3OsClose(pPager.sjfd);
			}
			//sqlite3_free( ref pPager.aSavepoint );
			pPager.aSavepoint = null;
			pPager.nSavepoint = 0;
			pPager.nSubRec = 0;
		}

		/*
		** Set the bit number pgno in the PagerSavepoint.pInSavepoint
		** bitvecs of all open savepoints. Return SQLITE_OK if successful
		** or SQLITE_NOMEM if a malloc failure occurs.
		*/

		private static int addToSavepointBitvecs(Pager pPager, u32 pgno)
		{
			int ii;                   /* Loop counter */
			int rc = SQLITE_OK;       /* Result code */

			for (ii = 0; ii < pPager.nSavepoint; ii++)
			{
				PagerSavepoint p = pPager.aSavepoint[ii];
				if (pgno <= p.nOrig)
				{
					rc |= sqlite3BitvecSet(p.pInSavepoint, pgno);
					testcase(rc == SQLITE_NOMEM);
					Debug.Assert(rc == SQLITE_OK || rc == SQLITE_NOMEM);
				}
			}
			return rc;
		}

		/*
		** This function is a no-op if the pager is in exclusive mode and not
		** in the ERROR state. Otherwise, it switches the pager to PAGER_OPEN
		** state.
		**
		** If the pager is not in exclusive-access mode, the database file is
		** completely unlocked. If the file is unlocked and the file-system does
		** not exhibit the UNDELETABLE_WHEN_OPEN property, the journal file is
		** closed (if it is open).
		**
		** If the pager is in ERROR state when this function is called, the
		** contents of the pager cache are discarded before switching back to
		** the OPEN state. Regardless of whether the pager is in exclusive-mode
		** or not, any journal file left in the file-system will be treated
		** as a hot-journal and rolled back the next time a read-transaction
		** is opened (by this or by any other connection).
		*/

		private static void pager_unlock(Pager pPager)
		{
			Debug.Assert(pPager.eState == PAGER_READER
			|| pPager.eState == PAGER_OPEN
			|| pPager.eState == PAGER_ERROR
			);

			sqlite3BitvecDestroy(ref pPager.pInJournal);
			pPager.pInJournal = null;
			releaseAllSavepoints(pPager);

			if (pagerUseWal(pPager))
			{
				Debug.Assert(!isOpen(pPager.jfd));
				sqlite3WalEndReadTransaction(pPager.pWal);
				pPager.eState = PAGER_OPEN;
			}
			else if (!pPager.exclusiveMode)
			{
				int rc;                       /* Error code returned by pagerUnlockDb() */
				int iDc = isOpen(pPager.fd) ? sqlite3OsDeviceCharacteristics(pPager.fd) : 0;

				/* If the operating system support deletion of open files, then
				** close the journal file when dropping the database lock.  Otherwise
				** another connection with journal_mode=delete might delete the file
				** out from under us.
				*/
				Debug.Assert((PAGER_JOURNALMODE_MEMORY & 5) != 1);
				Debug.Assert((PAGER_JOURNALMODE_OFF & 5) != 1);
				Debug.Assert((PAGER_JOURNALMODE_WAL & 5) != 1);
				Debug.Assert((PAGER_JOURNALMODE_DELETE & 5) != 1);
				Debug.Assert((PAGER_JOURNALMODE_TRUNCATE & 5) == 1);
				Debug.Assert((PAGER_JOURNALMODE_PERSIST & 5) == 1);
				if (0 == (iDc & SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN)
				|| 1 != (pPager.journalMode & 5)
				)
				{
					sqlite3OsClose(pPager.jfd);
				}

				/* If the pager is in the ERROR state and the call to unlock the database
				** file fails, set the current lock to UNKNOWN_LOCK. See the comment
				** above the #define for UNKNOWN_LOCK for an explanation of why this
				** is necessary.
				*/
				rc = pagerUnlockDb(pPager, NO_LOCK);
				if (rc != SQLITE_OK && pPager.eState == PAGER_ERROR)
				{
					pPager.eLock = UNKNOWN_LOCK;
				}

				/* The pager state may be changed from PAGER_ERROR to PAGER_OPEN here
				** without clearing the error code. This is intentional - the error
				** code is cleared and the cache reset in the block below.
				*/
				Debug.Assert(pPager.errCode != 0 || pPager.eState != PAGER_ERROR);
				pPager.changeCountDone = false;
				pPager.eState = PAGER_OPEN;
			}

			/* If Pager.errCode is set, the contents of the pager cache cannot be
			** trusted. Now that there are no outstanding references to the pager,
			** it can safely move back to PAGER_OPEN state. This happens in both
			** normal and exclusive-locking mode.
			*/
			if (pPager.errCode != 0)
			{
				Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
0 == pPager.memDb
#endif
);
				pager_reset(pPager);
				pPager.changeCountDone = pPager.tempFile;
				pPager.eState = PAGER_OPEN;
				pPager.errCode = SQLITE_OK;
			}

			pPager.journalOff = 0;
			pPager.journalHdr = 0;
			pPager.setMaster = 0;
		}

		/*
		** This function is called whenever an IOERR or FULL error that requires
		** the pager to transition into the ERROR state may ahve occurred.
		** The first argument is a pointer to the pager structure, the second
		** the error-code about to be returned by a pager API function. The
		** value returned is a copy of the second argument to this function.
		**
		** If the second argument is SQLITE_FULL, SQLITE_IOERR or one of the
		** IOERR sub-codes, the pager enters the ERROR state and the error code
		** is stored in Pager.errCode. While the pager remains in the ERROR state,
		** all major API calls on the Pager will immediately return Pager.errCode.
		**
		** The ERROR state indicates that the contents of the pager-cache
		** cannot be trusted. This state can be cleared by completely discarding
		** the contents of the pager-cache. If a transaction was active when
		** the persistent error occurred, then the rollback journal may need
		** to be replayed to restore the contents of the database file (as if
		** it were a hot-journal).
		*/

		private static int pager_error(Pager pPager, int rc)
		{
			int rc2 = rc & 0xff;
			Debug.Assert(rc == SQLITE_OK ||
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
 0 == pPager.memDb
#endif
);
			Debug.Assert(
			pPager.errCode == SQLITE_FULL ||
			pPager.errCode == SQLITE_OK ||
			(pPager.errCode & 0xff) == SQLITE_IOERR
			);
			if (
			rc2 == SQLITE_FULL || rc2 == SQLITE_IOERR)
			{
				pPager.errCode = rc;
				pPager.eState = PAGER_ERROR;
			}
			return rc;
		}

		/*
		** This routine ends a transaction. A transaction is usually ended by
		** either a COMMIT or a ROLLBACK operation. This routine may be called
		** after rollback of a hot-journal, or if an error occurs while opening
		** the journal file or writing the very first journal-header of a
		** database transaction.
		**
		** This routine is never called in PAGER_ERROR state. If it is called
		** in PAGER_NONE or PAGER_SHARED state and the lock held is less
		** exclusive than a RESERVED lock, it is a no-op.
		**
		** Otherwise, any active savepoints are released.
		**
		** If the journal file is open, then it is "finalized". Once a journal
		** file has been finalized it is not possible to use it to roll back a
		** transaction. Nor will it be considered to be a hot-journal by this
		** or any other database connection. Exactly how a journal is finalized
		** depends on whether or not the pager is running in exclusive mode and
		** the current journal-mode (Pager.journalMode value), as follows:
		**
		**   journalMode==MEMORY
		**     Journal file descriptor is simply closed. This destroys an
		**     in-memory journal.
		**
		**   journalMode==TRUNCATE
		**     Journal file is truncated to zero bytes in size.
		**
		**   journalMode==PERSIST
		**     The first 28 bytes of the journal file are zeroed. This invalidates
		**     the first journal header in the file, and hence the entire journal
		**     file. An invalid journal file cannot be rolled back.
		**
		**   journalMode==DELETE
		**     The journal file is closed and deleted using sqlite3OsDelete().
		**
		**     If the pager is running in exclusive mode, this method of finalizing
		**     the journal file is never used. Instead, if the journalMode is
		**     DELETE and the pager is in exclusive mode, the method described under
		**     journalMode==PERSIST is used instead.
		**
		** After the journal is finalized, the pager moves to PAGER_READER state.
		** If running in non-exclusive rollback mode, the lock on the file is
		** downgraded to a SHARED_LOCK.
		**
		** SQLITE_OK is returned if no error occurs. If an error occurs during
		** any of the IO operations to finalize the journal file or unlock the
		** database then the IO error code is returned to the user. If the
		** operation to finalize the journal file fails, then the code still
		** tries to unlock the database file if not in exclusive mode. If the
		** unlock operation fails as well, then the first error code related
		** to the first error encountered (the journal finalization one) is
		** returned.
		*/

		private static int pager_end_transaction(Pager pPager, int hasMaster)
		{
			int rc = SQLITE_OK;     /* Error code from journal finalization operation */
			int rc2 = SQLITE_OK;    /* Error code from db file unlock operation */
			/* Do nothing if the pager does not have an open write transaction
			** or at least a RESERVED lock. This function may be called when there
			** is no write-transaction active but a RESERVED or greater lock is
			** held under two circumstances:
			**
			**   1. After a successful hot-journal rollback, it is called with
			**      eState==PAGER_NONE and eLock==EXCLUSIVE_LOCK.
			**
			**   2. If a connection with locking_mode=exclusive holding an EXCLUSIVE
			**      lock switches back to locking_mode=normal and then executes a
			**      read-transaction, this function is called with eState==PAGER_READER
			**      and eLock==EXCLUSIVE_LOCK when the read-transaction is closed.
			*/
			Debug.Assert(assert_pager_state(pPager));
			Debug.Assert(pPager.eState != PAGER_ERROR);
			if (pPager.eState < PAGER_WRITER_LOCKED && pPager.eLock < RESERVED_LOCK)
			{
				return SQLITE_OK;
			}

			releaseAllSavepoints(pPager);
			Debug.Assert(isOpen(pPager.jfd) || pPager.pInJournal == null);
			if (isOpen(pPager.jfd))
			{
				Debug.Assert(!pagerUseWal(pPager));

				/* Finalize the journal file. */
				if (sqlite3IsMemJournal(pPager.jfd))
				{
					Debug.Assert(pPager.journalMode == PAGER_JOURNALMODE_MEMORY);
					sqlite3OsClose(pPager.jfd);
				}
				else if (pPager.journalMode == PAGER_JOURNALMODE_TRUNCATE)
				{
					if (pPager.journalOff == 0)
					{
						rc = SQLITE_OK;
					}
					else
					{
						rc = sqlite3OsTruncate(pPager.jfd, 0);
					}
					pPager.journalOff = 0;
				}
				else if (pPager.journalMode == PAGER_JOURNALMODE_PERSIST
				|| (pPager.exclusiveMode && pPager.journalMode != PAGER_JOURNALMODE_WAL)
				)
				{
					rc = zeroJournalHdr(pPager, hasMaster);
					pPager.journalOff = 0;
				}
				else
				{
					/* This branch may be executed with Pager.journalMode==MEMORY if
					** a hot-journal was just rolled back. In this case the journal
					** file should be closed and deleted. If this connection writes to
					** the database file, it will do so using an in-memory journal.
					*/
					Debug.Assert(pPager.journalMode == PAGER_JOURNALMODE_DELETE
					|| pPager.journalMode == PAGER_JOURNALMODE_MEMORY
					|| pPager.journalMode == PAGER_JOURNALMODE_WAL
					);
					sqlite3OsClose(pPager.jfd);
					if (!pPager.tempFile)
					{
						rc = sqlite3OsDelete(pPager.pVfs, pPager.zJournal, 0);
					}
				}
			}
#if SQLITE_CHECK_PAGES
sqlite3PcacheIterateDirty(pPager.pPCache, pager_set_pagehash);
if( pPager.dbSize==0 && sqlite3PcacheRefCount(pPager.pPCache)>0 ){
PgHdr p = pager_lookup(pPager, 1);
if( p != null ){
p.pageHash = null;
sqlite3PagerUnref(p);
}
}
#endif
			sqlite3BitvecDestroy(ref pPager.pInJournal);
			pPager.pInJournal = null;
			pPager.nRec = 0;
			sqlite3PcacheCleanAll(pPager.pPCache);
			sqlite3PcacheTruncate(pPager.pPCache, pPager.dbSize);

			if (pagerUseWal(pPager))
			{
				/* Drop the WAL write-lock, if any. Also, if the connection was in
				** locking_mode=exclusive mode but is no longer, drop the EXCLUSIVE
				** lock held on the database file.
				*/
				rc2 = sqlite3WalEndWriteTransaction(pPager.pWal);
				Debug.Assert(rc2 == SQLITE_OK);
			}
			if (!pPager.exclusiveMode
			&& (!pagerUseWal(pPager) || sqlite3WalExclusiveMode(pPager.pWal, 0))
			)
			{
				rc2 = pagerUnlockDb(pPager, SHARED_LOCK);
				pPager.changeCountDone = false;
			}
			pPager.eState = PAGER_READER;
			pPager.setMaster = 0;

			return (rc == SQLITE_OK ? rc2 : rc);
		}

		/*
		** Execute a rollback if a transaction is active and unlock the
		** database file.
		**
		** If the pager has already entered the ERROR state, do not attempt
		** the rollback at this time. Instead, pager_unlock() is called. The
		** call to pager_unlock() will discard all in-memory pages, unlock
		** the database file and move the pager back to OPEN state. If this
		** means that there is a hot-journal left in the file-system, the next
		** connection to obtain a shared lock on the pager (which may be this one)
		** will roll it back.
		**
		** If the pager has not already entered the ERROR state, but an IO or
		** malloc error occurs during a rollback, then this will itself cause
		** the pager to enter the ERROR state. Which will be cleared by the
		** call to pager_unlock(), as described above.
		*/

		private static void pagerUnlockAndRollback(Pager pPager)
		{
			if (pPager.eState != PAGER_ERROR && pPager.eState != PAGER_OPEN)
			{
				Debug.Assert(assert_pager_state(pPager));
				if (pPager.eState >= PAGER_WRITER_LOCKED)
				{
					sqlite3BeginBenignMalloc();
					sqlite3PagerRollback(pPager);
					sqlite3EndBenignMalloc();
				}
				else if (!pPager.exclusiveMode)
				{
					Debug.Assert(pPager.eState == PAGER_READER);
					pager_end_transaction(pPager, 0);
				}
			}
			pager_unlock(pPager);
		}

		/*
		** Parameter aData must point to a buffer of pPager.pageSize bytes
		** of data. Compute and return a checksum based ont the contents of the
		** page of data and the current value of pPager.cksumInit.
		**
		** This is not a real checksum. It is really just the sum of the
		** random initial value (pPager.cksumInit) and every 200th byte
		** of the page data, starting with byte offset (pPager.pageSize%200).
		** Each byte is interpreted as an 8-bit unsigned integer.
		**
		** Changing the formula used to compute this checksum results in an
		** incompatible journal file format.
		**
		** If journal corruption occurs due to a power failure, the most likely
		** scenario is that one end or the other of the record will be changed.
		** It is much less likely that the two ends of the journal record will be
		** correct and the middle be corrupt.  Thus, this "checksum" scheme,
		** though fast and simple, catches the mostly likely kind of corruption.
		*/

		private static u32 pager_cksum(Pager pPager, byte[] aData)
		{
			u32 cksum = pPager.cksumInit;         /* Checksum value to return */
			int i = pPager.pageSize - 200;        /* Loop counter */
			while (i > 0)
			{
				cksum += aData[i];
				i -= 200;
			}
			return cksum;
		}

		/*
		** Report the current page size and number of reserved bytes back
		** to the codec.
		*/
#if SQLITE_HAS_CODEC

		private static void pagerReportSize(Pager pPager)
		{
			if (pPager.xCodecSizeChng != null)
			{
				pPager.xCodecSizeChng(pPager.pCodec, pPager.pageSize,
				pPager.nReserve);
			}
		}

#else
//# define pagerReportSize(X)     /* No-op if we do not support a codec */
static void pagerReportSize(Pager X){}
#endif

		/*
** Read a single page from either the journal file (if isMainJrnl==1) or
** from the sub-journal (if isMainJrnl==0) and playback that page.
** The page begins at offset *pOffset into the file. The *pOffset
** value is increased to the start of the next page in the journal.
**
** The main rollback journal uses checksums - the statement journal does
** not.
**
** If the page number of the page record read from the (sub-)journal file
** is greater than the current value of Pager.dbSize, then playback is
** skipped and SQLITE_OK is returned.
**
** If pDone is not NULL, then it is a record of pages that have already
** been played back.  If the page at *pOffset has already been played back
** (if the corresponding pDone bit is set) then skip the playback.
** Make sure the pDone bit corresponding to the *pOffset page is set
** prior to returning.
**
** If the page record is successfully read from the (sub-)journal file
** and played back, then SQLITE_OK is returned. If an IO error occurs
** while reading the record from the (sub-)journal file or while writing
** to the database file, then the IO error code is returned. If data
** is successfully read from the (sub-)journal file but appears to be
** corrupted, SQLITE_DONE is returned. Data is considered corrupted in
** two circumstances:
**
**   * If the record page-number is illegal (0 or PAGER_MJ_PGNO), or
**   * If the record is being rolled back from the main journal file
**     and the checksum field does not match the record content.
**
** Neither of these two scenarios are possible during a savepoint rollback.
**
** If this is a savepoint rollback, then memory may have to be dynamically
** allocated by this function. If this is the case and an allocation fails,
** SQLITE_NOMEM is returned.
*/

		private static int pager_playback_one_page(
		Pager pPager,                /* The pager being played back */
		ref i64 pOffset,             /* Offset of record to playback */
		Bitvec pDone,                /* Bitvec of pages already played back */
		int isMainJrnl,              /* True for main rollback journal. False for Stmt jrnl */
		int isSavepnt                /* True for a savepoint rollback */
		)
		{
			int rc;
			PgHdr pPg;                    /* An existing page in the cache */
			Pgno pgno = 0;                /* The page number of a page in journal */
			u32 cksum = 0;                /* Checksum used for sanity checking */
			byte[] aData;                 /* Temporary storage for the page */
			sqlite3_file jfd;             /* The file descriptor for the journal file */
			bool isSynced;                /* True if journal page is synced */

			Debug.Assert((isMainJrnl & ~1) == 0);   /* isMainJrnl is 0 or 1 */
			Debug.Assert((isSavepnt & ~1) == 0);    /* isSavepnt is 0 or 1 */
			Debug.Assert(isMainJrnl != 0 || pDone != null);        /* pDone always used on sub-journals */
			Debug.Assert(isSavepnt != 0 || pDone == null);    /* pDone never used on non-savepoint */

			aData = pPager.pTmpSpace;
			Debug.Assert(aData != null);         /* Temp storage must have already been allocated */
			Debug.Assert(pagerUseWal(pPager) == false || (0 == isMainJrnl && isSavepnt != 0));

			/* Either the state is greater than PAGER_WRITER_CACHEMOD (a transaction
			** or savepoint rollback done at the request of the caller) or this is
			** a hot-journal rollback. If it is a hot-journal rollback, the pager
			** is in state OPEN and holds an EXCLUSIVE lock. Hot-journal rollback
			** only reads from the main journal, not the sub-journal.
			*/
			Debug.Assert(pPager.eState >= PAGER_WRITER_CACHEMOD
			|| (pPager.eState == PAGER_OPEN && pPager.eLock == EXCLUSIVE_LOCK)
			);
			Debug.Assert(pPager.eState >= PAGER_WRITER_CACHEMOD || isMainJrnl != 0);

			/* Read the page number and page data from the journal or sub-journal
			** file. Return an error code to the caller if an IO error occurs.
			*/
			jfd = isMainJrnl != 0 ? pPager.jfd : pPager.sjfd;

			rc = read32bits(jfd, pOffset, ref pgno);
			if (rc != SQLITE_OK)
				return rc;
			rc = sqlite3OsRead(jfd, aData, pPager.pageSize, (pOffset) + 4);
			if (rc != SQLITE_OK)
				return rc;
			pOffset += pPager.pageSize + 4 + isMainJrnl * 4;

			/* Sanity checking on the page.  This is more important that I originally
			** thought.  If a power failure occurs while the journal is being written,
			** it could cause invalid data to be written into the journal.  We need to
			** detect this invalid data (with high probability) and ignore it.
			*/
			if (pgno == 0 || pgno == PAGER_MJ_PGNO(pPager))
			{
				Debug.Assert(0 == isSavepnt);
				return SQLITE_DONE;
			}
			if (pgno > pPager.dbSize || sqlite3BitvecTest(pDone, pgno) != 0)
			{
				return SQLITE_OK;
			}
			if (isMainJrnl != 0)
			{
				rc = read32bits(jfd, (pOffset) - 4, ref cksum);
				if (rc != 0)
					return rc;
				if (0 == isSavepnt && pager_cksum(pPager, aData) != cksum)
				{
					return SQLITE_DONE;
				}
			}

			/* If this page has already been played by before during the current
			** rollback, then don't bother to play it back again.
			*/
			if (pDone != null && (rc = sqlite3BitvecSet(pDone, pgno)) != SQLITE_OK)
			{
				return rc;
			}

			/* When playing back page 1, restore the nReserve setting
			*/
			if (pgno == 1 && pPager.nReserve != (aData)[20])
			{
				pPager.nReserve = (aData)[20];
				pagerReportSize(pPager);
			}

			/* If the pager is in CACHEMOD state, then there must be a copy of this
			** page in the pager cache. In this case just update the pager cache,
			** not the database file. The page is left marked dirty in this case.
			**
			** An exception to the above rule: If the database is in no-sync mode
			** and a page is moved during an incremental vacuum then the page may
			** not be in the pager cache. Later: if a malloc() or IO error occurs
			** during a Movepage() call, then the page may not be in the cache
			** either. So the condition described in the above paragraph is not
			** assert()able.
			**
			** If in WRITER_DBMOD, WRITER_FINISHED or OPEN state, then we update the
			** pager cache if it exists and the main file. The page is then marked
			** not dirty. Since this code is only executed in PAGER_OPEN state for
			** a hot-journal rollback, it is guaranteed that the page-cache is empty
			** if the pager is in OPEN state.
			**
			** Ticket #1171:  The statement journal might contain page content that is
			** different from the page content at the start of the transaction.
			** This occurs when a page is changed prior to the start of a statement
			** then changed again within the statement.  When rolling back such a
			** statement we must not write to the original database unless we know
			** for certain that original page contents are synced into the main rollback
			** journal.  Otherwise, a power loss might leave modified data in the
			** database file without an entry in the rollback journal that can
			** restore the database to its original form.  Two conditions must be
			** met before writing to the database files. (1) the database must be
			** locked.  (2) we know that the original page content is fully synced
			** in the main journal either because the page is not in cache or else
			** the page is marked as needSync==0.
			**
			** 2008-04-14:  When attempting to vacuum a corrupt database file, it
			** is possible to fail a statement on a database that does not yet exist.
			** Do not attempt to write if database file has never been opened.
			*/
			if (pagerUseWal(pPager))
			{
				pPg = null;
			}
			else
			{
				pPg = pager_lookup(pPager, pgno);
			}
			Debug.Assert(pPg != null ||
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
 pPager.memDb == 0
#endif
);
			Debug.Assert(pPager.eState != PAGER_OPEN || pPg == null);

			PAGERTRACE("PLAYBACK %d page %d hash(%08x) %s\n",
			PAGERID(pPager), pgno, pager_datahash(pPager.pageSize, aData),
			(isMainJrnl != 0 ? "main-journal" : "sub-journal")
			);
			if (isMainJrnl != 0)
			{
				isSynced = pPager.noSync || (pOffset <= pPager.journalHdr);
			}
			else
			{
				isSynced = (pPg == null || 0 == (pPg.flags & PGHDR_NEED_SYNC));
			}
			if (isOpen(pPager.fd)
			&& (pPager.eState >= PAGER_WRITER_DBMOD || pPager.eState == PAGER_OPEN)
			&& isSynced
			)
			{
				i64 ofst = (pgno - 1) * pPager.pageSize;
				testcase(0 == isSavepnt && pPg != null && (pPg.flags & PGHDR_NEED_SYNC) != 0);
				Debug.Assert(!pagerUseWal(pPager));
				rc = sqlite3OsWrite(pPager.fd, aData, pPager.pageSize, ofst);
				if (pgno > pPager.dbFileSize)
				{
					pPager.dbFileSize = pgno;
				}
				if (pPager.pBackup != null)
				{
					if (CODEC1(pPager, aData, pgno, SQLITE_DECRYPT))
						rc = SQLITE_NOMEM; // CODEC1( pPager, aData, pgno, 3, rc = SQLITE_NOMEM );
					sqlite3BackupUpdate(pPager.pBackup, pgno, (u8[])aData);
					if (CODEC2(pPager, aData, pgno, SQLITE_ENCRYPT_READ_CTX, ref aData))
						rc = SQLITE_NOMEM;//CODEC2( pPager, aData, pgno, 7, rc = SQLITE_NOMEM, aData);
				}
			}
			else if (0 == isMainJrnl && pPg == null)
			{
				/* If this is a rollback of a savepoint and data was not written to
				** the database and the page is not in-memory, there is a potential
				** problem. When the page is next fetched by the b-tree layer, it
				** will be read from the database file, which may or may not be
				** current.
				**
				** There are a couple of different ways this can happen. All are quite
				** obscure. When running in synchronous mode, this can only happen
				** if the page is on the free-list at the start of the transaction, then
				** populated, then moved using sqlite3PagerMovepage().
				**
				** The solution is to add an in-memory page to the cache containing
				** the data just read from the sub-journal. Mark the page as dirty
				** and if the pager requires a journal-sync, then mark the page as
				** requiring a journal-sync before it is written.
				*/
				Debug.Assert(isSavepnt != 0);
				Debug.Assert(pPager.doNotSpill == 0);
				pPager.doNotSpill++;
				rc = sqlite3PagerAcquire(pPager, pgno, ref pPg, 1);
				Debug.Assert(pPager.doNotSpill == 1);
				pPager.doNotSpill--;
				if (rc != SQLITE_OK)
					return rc;
				pPg.flags &= ~PGHDR_NEED_READ;
				sqlite3PcacheMakeDirty(pPg);
			}
			if (pPg != null)
			{
				/* No page should ever be explicitly rolled back that is in use, except
				** for page 1 which is held in use in order to keep the lock on the
				** database active. However such a page may be rolled back as a result
				** of an internal error resulting in an automatic call to
				** sqlite3PagerRollback().
				*/
				byte[] pData = pPg.pData;
				Buffer.BlockCopy(aData, 0, pData, 0, pPager.pageSize);// memcpy(pData, (u8[])aData, pPager.pageSize);
				pPager.xReiniter(pPg);
				if (isMainJrnl != 0 && (0 == isSavepnt || pOffset <= pPager.journalHdr))
				{
					/* If the contents of this page were just restored from the main
					** journal file, then its content must be as they were when the
					** transaction was first opened. In this case we can mark the page
					** as clean, since there will be no need to write it out to the
					** database.
					**
					** There is one exception to this rule. If the page is being rolled
					** back as part of a savepoint (or statement) rollback from an
					** unsynced portion of the main journal file, then it is not safe
					** to mark the page as clean. This is because marking the page as
					** clean will clear the PGHDR_NEED_SYNC flag. Since the page is
					** already in the journal file (recorded in Pager.pInJournal) and
					** the PGHDR_NEED_SYNC flag is cleared, if the page is written to
					** again within this transaction, it will be marked as dirty but
					** the PGHDR_NEED_SYNC flag will not be set. It could then potentially
					** be written out into the database file before its journal file
					** segment is synced. If a crash occurs during or following this,
					** database corruption may ensue.
					*/
					Debug.Assert(!pagerUseWal(pPager));
					sqlite3PcacheMakeClean(pPg);
				}
				pager_set_pagehash(pPg);
				/* If this was page 1, then restore the value of Pager.dbFileVers.
				** Do this before any decoding. */
				if (pgno == 1)
				{
					Buffer.BlockCopy(pData, 24, pPager.dbFileVers, 0, pPager.dbFileVers.Length); //memcpy(pPager.dbFileVers, ((u8*)pData)[24], sizeof(pPager.dbFileVers));
				}

				/* Decode the page just read from disk */
				if (CODEC1(pPager, pData, pPg.pgno, SQLITE_DECRYPT))
					rc = SQLITE_NOMEM; //CODEC1(pPager, pData, pPg.pgno, 3, rc=SQLITE_NOMEM);
				sqlite3PcacheRelease(pPg);
			}
			return rc;
		}

		/*
		** Parameter zMaster is the name of a master journal file. A single journal
		** file that referred to the master journal file has just been rolled back.
		** This routine checks if it is possible to delete the master journal file,
		** and does so if it is.
		**
		** Argument zMaster may point to Pager.pTmpSpace. So that buffer is not
		** available for use within this function.
		**
		** When a master journal file is created, it is populated with the names
		** of all of its child journals, one after another, formatted as utf-8
		** encoded text. The end of each child journal file is marked with a
		** nul-terminator byte (0x00). i.e. the entire contents of a master journal
		** file for a transaction involving two databases might be:
		**
		**   "/home/bill/a.db-journal\x00/home/bill/b.db-journal\x00"
		**
		** A master journal file may only be deleted once all of its child
		** journals have been rolled back.
		**
		** This function reads the contents of the master-journal file into
		** memory and loops through each of the child journal names. For
		** each child journal, it checks if:
		**
		**   * if the child journal exists, and if so
		**   * if the child journal contains a reference to master journal
		**     file zMaster
		**
		** If a child journal can be found that matches both of the criteria
		** above, this function returns without doing anything. Otherwise, if
		** no such child journal can be found, file zMaster is deleted from
		** the file-system using sqlite3OsDelete().
		**
		** If an IO error within this function, an error code is returned. This
		** function allocates memory by calling sqlite3Malloc(). If an allocation
		** fails, SQLITE_NOMEM is returned. Otherwise, if no IO or malloc errors
		** occur, SQLITE_OK is returned.
		**
		** TODO: This function allocates a single block of memory to load
		** the entire contents of the master journal file. This could be
		** a couple of kilobytes or so - potentially larger than the page
		** size.
		*/

		private static int pager_delmaster(Pager pPager, string zMaster)
		{
			sqlite3_vfs pVfs = pPager.pVfs;
			int rc;                       /* Return code */
			sqlite3_file pMaster;         /* Malloc'd master-journal file descriptor */
			sqlite3_file pJournal;        /* Malloc'd child-journal file descriptor */
			//string zMasterJournal = null; /* Contents of master journal file */
			i64 nMasterJournal;           /* Size of master journal file */
			string zJournal;              /* Pointer to one journal within MJ file */
			string zMasterPtr;            /* Space to hold MJ filename from a journal file */
			int nMasterPtr;               /* Amount of space allocated to zMasterPtr[] */

			/* Allocate space for both the pJournal and pMaster file descriptors.
			** If successful, open the master journal file for reading.
			*/
			pMaster = new sqlite3_file();// (sqlite3_file*)sqlite3MallocZero( pVfs.szOsFile * 2 );
			pJournal = new sqlite3_file();// (sqlite3_file*)( ( (u8*)pMaster ) + pVfs.szOsFile );
			//if ( null == pMaster )
			//{
			//  rc = SQLITE_NOMEM;
			//}
			//else
			{
				const int flags = (SQLITE_OPEN_READONLY | SQLITE_OPEN_MASTER_JOURNAL);
				int iDummy = 0;
				rc = sqlite3OsOpen(pVfs, zMaster, pMaster, flags, ref iDummy);
			}
			if (rc != SQLITE_OK)
				goto delmaster_out;

			Debugger.Break();    //TODO --

			/* Load the entire master journal file into space obtained from
			** sqlite3_malloc() and pointed to by zMasterJournal.   Also obtain
			** sufficient space (in zMasterPtr) to hold the names of master
			** journal files extracted from regular rollback-journals.
			*/
			//rc = sqlite3OsFileSize(pMaster, &nMasterJournal);
			//if (rc != SQLITE_OK) goto delmaster_out;
			//nMasterPtr = pVfs.mxPathname + 1;
			//  zMasterJournal = sqlite3Malloc((int)nMasterJournal + nMasterPtr + 1);
			//  if ( !zMasterJournal )
			//  {
			//    rc = SQLITE_NOMEM;
			//    goto delmaster_out;
			//  }
			//  zMasterPtr = &zMasterJournal[nMasterJournal+1];
			//  rc = sqlite3OsRead( pMaster, zMasterJournal, (int)nMasterJournal, 0 );
			//  if ( rc != SQLITE_OK ) goto delmaster_out;
			//  zMasterJournal[nMasterJournal] = 0;

			//  zJournal = zMasterJournal;
			//  while ( ( zJournal - zMasterJournal ) < nMasterJournal )
			//  {
			//    int exists;
			//    rc = sqlite3OsAccess( pVfs, zJournal, SQLITE_ACCESS_EXISTS, &exists );
			//    if ( rc != SQLITE_OK )
			//    {
			//      goto delmaster_out;
			//    }
			//    if ( exists )
			//    {
			//      /* One of the journals pointed to by the master journal exists.
			//      ** Open it and check if it points at the master journal. If
			//      ** so, return without deleting the master journal file.
			//      */
			//      int c;
			//      int flags = ( SQLITE_OPEN_READONLY | SQLITE_OPEN_MAIN_JOURNAL );
			//      rc = sqlite3OsOpen( pVfs, zJournal, pJournal, flags, 0 );
			//      if ( rc != SQLITE_OK )
			//      {
			//        goto delmaster_out;
			//      }

			//      rc = readMasterJournal( pJournal, zMasterPtr, nMasterPtr );
			//      sqlite3OsClose( pJournal );
			//      if ( rc != SQLITE_OK )
			//      {
			//        goto delmaster_out;
			//      }

			//      c = zMasterPtr[0] != 0 && strcmp( zMasterPtr, zMaster ) == 0;
			//      if ( c )
			//      {
			//        /* We have a match. Do not delete the master journal file. */
			//        goto delmaster_out;
			//      }
			//    }
			//    zJournal += ( sqlite3Strlen30( zJournal ) + 1 );
			//   }
			//
			//sqlite3OsClose(pMaster);
			//rc = sqlite3OsDelete( pVfs, zMaster, 0 );

			goto delmaster_out;
		delmaster_out:
			//sqlite3_free( ref zMasterJournal );
			if (pMaster != null)
			{
				sqlite3OsClose(pMaster);
				Debug.Assert(!isOpen(pJournal));
				//sqlite3_free( ref pMaster );
			}
			return rc;
		}

		/*
		** This function is used to change the actual size of the database
		** file in the file-system. This only happens when committing a transaction,
		** or rolling back a transaction (including rolling back a hot-journal).
		**
		** If the main database file is not open, or the pager is not in either
		** DBMOD or OPEN state, this function is a no-op. Otherwise, the size
		** of the file is changed to nPage pages (nPage*pPager.pageSize bytes).
		** If the file on disk is currently larger than nPage pages, then use the VFS
		** xTruncate() method to truncate it.
		**
		** Or, it might might be the case that the file on disk is smaller than
		** nPage pages. Some operating system implementations can get confused if
		** you try to truncate a file to some size that is larger than it
		** currently is, so detect this case and write a single zero byte to
		** the end of the new file instead.
		**
		** If successful, return SQLITE_OK. If an IO error occurs while modifying
		** the database file, return the error code to the caller.
		*/

		private static int pager_truncate(Pager pPager, u32 nPage)
		{
			int rc = SQLITE_OK;
			Debug.Assert(pPager.eState != PAGER_ERROR);
			Debug.Assert(pPager.eState != PAGER_READER);

			if (isOpen(pPager.fd)
			&& (pPager.eState >= PAGER_WRITER_DBMOD || pPager.eState == PAGER_OPEN)
			)
			{
				i64 currentSize = 0, newSize;
				int szPage = pPager.pageSize;
				Debug.Assert(pPager.eLock == EXCLUSIVE_LOCK);
				/* TODO: Is it safe to use Pager.dbFileSize here? */
				rc = sqlite3OsFileSize(pPager.fd, ref currentSize);
				newSize = szPage * nPage;
				if (rc == SQLITE_OK && currentSize != newSize)
				{
					if (currentSize > newSize)
					{
						rc = sqlite3OsTruncate(pPager.fd, newSize);
					}
					else
					{
						byte[] pTmp = pPager.pTmpSpace;
						Array.Clear(pTmp, 0, szPage);//memset( pTmp, 0, szPage );
						testcase((newSize - szPage) < currentSize);
						testcase((newSize - szPage) == currentSize);
						testcase((newSize - szPage) > currentSize);
						rc = sqlite3OsWrite(pPager.fd, pTmp, szPage, newSize - szPage);
					}
					if (rc == SQLITE_OK)
					{
						pPager.dbSize = nPage;
					}
				}
			}
			return rc;
		}

		/*
		** Set the value of the Pager.sectorSize variable for the given
		** pager based on the value returned by the xSectorSize method
		** of the open database file. The sector size will be used used
		** to determine the size and alignment of journal header and
		** master journal pointers within created journal files.
		**
		** For temporary files the effective sector size is always 512 bytes.
		**
		** Otherwise, for non-temporary files, the effective sector size is
		** the value returned by the xSectorSize() method rounded up to 512 if
		** it is less than 32, or rounded down to MAX_SECTOR_SIZE if it
		** is greater than MAX_SECTOR_SIZE.
		*/

		private static void setSectorSize(Pager pPager)
		{
			Debug.Assert(isOpen(pPager.fd) || pPager.tempFile);
			if (!pPager.tempFile)
			{
				/* Sector size doesn't matter for temporary files. Also, the file
				** may not have been opened yet, in which case the OsSectorSize()
				** call will segfault.
				*/
				pPager.sectorSize = (u32)sqlite3OsSectorSize(pPager.fd);
			}
			if (pPager.sectorSize < 32)
			{
				Debug.Assert(MAX_SECTOR_SIZE >= 512);
				pPager.sectorSize = 512;
			}
			if (pPager.sectorSize > MAX_SECTOR_SIZE)
			{
				pPager.sectorSize = MAX_SECTOR_SIZE;
			}
		}

		/*
		** Playback the journal and thus restore the database file to
		** the state it was in before we started making changes.
		**
		** The journal file format is as follows:
		**
		**  (1)  8 byte prefix.  A copy of aJournalMagic[].
		**  (2)  4 byte big-endian integer which is the number of valid page records
		**       in the journal.  If this value is 0xffffffff, then compute the
		**       number of page records from the journal size.
		**  (3)  4 byte big-endian integer which is the initial value for the
		**       sanity checksum.
		**  (4)  4 byte integer which is the number of pages to truncate the
		**       database to during a rollback.
		**  (5)  4 byte big-endian integer which is the sector size.  The header
		**       is this many bytes in size.
		**  (6)  4 byte big-endian integer which is the page size.
		**  (7)  zero padding out to the next sector size.
		**  (8)  Zero or more pages instances, each as follows:
		**
		** When we speak of the journal header, we mean the first 7 items above.
		** Each entry in the journal is an instance of the 8th item.
		**
		** Call the value from the second bullet "nRec".  nRec is the number of
		** valid page entries in the journal.  In most cases, you can compute the
		** value of nRec from the size of the journal file.  But if a power
		** failure occurred while the journal was being written, it could be the
		** case that the size of the journal file had already been increased but
		** the extra entries had not yet made it safely to disk.  In such a case,
		** the value of nRec computed from the file size would be too large.  For
		** that reason, we always use the nRec value in the header.
		**
		** If the nRec value is 0xffffffff it means that nRec should be computed
		** from the file size.  This value is used when the user selects the
		** no-sync option for the journal.  A power failure could lead to corruption
		** in this case.  But for things like temporary table (which will be
		** deleted when the power is restored) we don't care.
		**
		** If the file opened as the journal file is not a well-formed
		** journal file then all pages up to the first corrupted page are rolled
		** back (or no pages if the journal header is corrupted). The journal file
		** is then deleted and SQLITE_OK returned, just as if no corruption had
		** been encountered.
		**
		** If an I/O or malloc() error occurs, the journal-file is not deleted
		** and an error code is returned.
		**
		** The isHot parameter indicates that we are trying to rollback a journal
		** that might be a hot journal.  Or, it could be that the journal is
		** preserved because of JOURNALMODE_PERSIST or JOURNALMODE_TRUNCATE.
		** If the journal really is hot, reset the pager cache prior rolling
		** back any content.  If the journal is merely persistent, no reset is
		** needed.
		*/

		private static int pager_playback(Pager pPager, int isHot)
		{
			sqlite3_vfs pVfs = pPager.pVfs;
			i64 szJ = 0;            /* Size of the journal file in bytes */
			u32 nRec = 0;            /* Number of Records in the journal */
			u32 u;                   /* Unsigned loop counter */
			u32 mxPg = 0;            /* Size of the original file in pages */
			int rc;                  /* Result code of a subroutine */
			int res = 1;             /* Value returned by sqlite3OsAccess() */
			byte[] zMaster = null;   /* Name of master journal file if any */
			int needPagerReset;      /* True to reset page prior to first page rollback */

			/* Figure out how many records are in the journal.  Abort early if
			** the journal is empty.
			*/
			Debug.Assert(isOpen(pPager.jfd));
			rc = sqlite3OsFileSize(pPager.jfd, ref szJ);
			if (rc != SQLITE_OK)
			{
				goto end_playback;
			}

			/* Read the master journal name from the journal, if it is present.
			** If a master journal file name is specified, but the file is not
			** present on disk, then the journal is not hot and does not need to be
			** played back.
			**
			** TODO: Technically the following is an error because it assumes that
			** buffer Pager.pTmpSpace is (mxPathname+1) bytes or larger. i.e. that
			** (pPager.pageSize >= pPager.pVfs.mxPathname+1). Using os_unix.c,
			**  mxPathname is 512, which is the same as the minimum allowable value
			** for pageSize.
			*/
			zMaster = new byte[pPager.pVfs.mxPathname + 1];// pPager.pTmpSpace );
			rc = readMasterJournal(pPager.jfd, zMaster, (u32)pPager.pVfs.mxPathname + 1);
			if (rc == SQLITE_OK && zMaster[0] != 0)
			{
				rc = sqlite3OsAccess(pVfs, Encoding.UTF8.GetString(zMaster, 0, zMaster.Length), SQLITE_ACCESS_EXISTS, ref res);
			}
			zMaster = null;
			if (rc != SQLITE_OK || res == 0)
			{
				goto end_playback;
			}
			pPager.journalOff = 0;
			needPagerReset = isHot;

			/* This loop terminates either when a readJournalHdr() or
			** pager_playback_one_page() call returns SQLITE_DONE or an IO error
			** occurs.
			*/
			while (true)
			{
				/* Read the next journal header from the journal file.  If there are
				** not enough bytes left in the journal file for a complete header, or
				** it is corrupted, then a process must have failed while writing it.
				** This indicates nothing more needs to be rolled back.
				*/
				rc = readJournalHdr(pPager, isHot, szJ, out nRec, out mxPg);
				if (rc != SQLITE_OK)
				{
					if (rc == SQLITE_DONE)
					{
						rc = SQLITE_OK;
					}
					goto end_playback;
				}

				/* If nRec is 0xffffffff, then this journal was created by a process
				** working in no-sync mode. This means that the rest of the journal
				** file consists of pages, there are no more journal headers. Compute
				** the value of nRec based on this assumption.
				*/
				if (nRec == 0xffffffff)
				{
					Debug.Assert(pPager.journalOff == JOURNAL_HDR_SZ(pPager));
					nRec = (u32)((szJ - JOURNAL_HDR_SZ(pPager)) / JOURNAL_PG_SZ(pPager));
				}

				/* If nRec is 0 and this rollback is of a transaction created by this
				** process and if this is the final header in the journal, then it means
				** that this part of the journal was being filled but has not yet been
				** synced to disk.  Compute the number of pages based on the remaining
				** size of the file.
				**
				** The third term of the test was added to fix ticket #2565.
				** When rolling back a hot journal, nRec==0 always means that the next
				** chunk of the journal contains zero pages to be rolled back.  But
				** when doing a ROLLBACK and the nRec==0 chunk is the last chunk in
				** the journal, it means that the journal might contain additional
				** pages that need to be rolled back and that the number of pages
				** should be computed based on the journal file size.
				*/
				if (nRec == 0 && 0 == isHot &&
				pPager.journalHdr + JOURNAL_HDR_SZ(pPager) == pPager.journalOff)
				{
					nRec = (u32)((szJ - pPager.journalOff) / JOURNAL_PG_SZ(pPager));
				}

				/* If this is the first header read from the journal, truncate the
				** database file back to its original size.
				*/
				if (pPager.journalOff == JOURNAL_HDR_SZ(pPager))
				{
					rc = pager_truncate(pPager, mxPg);
					if (rc != SQLITE_OK)
					{
						goto end_playback;
					}
					pPager.dbSize = mxPg;
				}

				/* Copy original pages out of the journal and back into the
				** database file and/or page cache.
				*/
				for (u = 0; u < nRec; u++)
				{
					if (needPagerReset != 0)
					{
						pager_reset(pPager);
						needPagerReset = 0;
					}
					rc = pager_playback_one_page(pPager, ref pPager.journalOff, null, 1, 0);
					if (rc != SQLITE_OK)
					{
						if (rc == SQLITE_DONE)
						{
							rc = SQLITE_OK;
							pPager.journalOff = szJ;
							break;
						}
						else if (rc == SQLITE_IOERR_SHORT_READ)
						{
							/* If the journal has been truncated, simply stop reading and
							** processing the journal. This might happen if the journal was
							** not completely written and synced prior to a crash.  In that
							** case, the database should have never been written in the
							** first place so it is OK to simply abandon the rollback. */
							rc = SQLITE_OK;
							goto end_playback;
						}
						else
						{
							/* If we are unable to rollback, quit and return the error
							** code.  This will cause the pager to enter the error state
							** so that no further harm will be done.  Perhaps the next
							** process to come along will be able to rollback the database.
							*/
							goto end_playback;
						}
					}
				}
			}
		/*NOTREACHED*/

		end_playback:
			/* Following a rollback, the database file should be back in its original
			** state prior to the start of the transaction, so invoke the
			** SQLITE_FCNTL_DB_UNCHANGED file-control method to disable the
			** assertion that the transaction counter was modified.
			*/
			sqlite3_int64 iDummy = 0;
			Debug.Assert(
			pPager.fd.pMethods == null ||
			sqlite3OsFileControl(pPager.fd, SQLITE_FCNTL_DB_UNCHANGED, ref iDummy) >= SQLITE_OK
			);

			/* If this playback is happening automatically as a result of an IO or
			** malloc error that occurred after the change-counter was updated but
			** before the transaction was committed, then the change-counter
			** modification may just have been reverted. If this happens in exclusive
			** mode, then subsequent transactions performed by the connection will not
			** update the change-counter at all. This may lead to cache inconsistency
			** problems for other processes at some point in the future. So, just
			** in case this has happened, clear the changeCountDone flag now.
			*/
			pPager.changeCountDone = pPager.tempFile;

			if (rc == SQLITE_OK)
			{
				zMaster = new byte[pPager.pVfs.mxPathname + 1];//pPager.pTmpSpace );
				rc = readMasterJournal(pPager.jfd, zMaster, (u32)pPager.pVfs.mxPathname + 1);
				testcase(rc != SQLITE_OK);
			}
			if (rc == SQLITE_OK
			&& (pPager.eState >= PAGER_WRITER_DBMOD || pPager.eState == PAGER_OPEN)
			)
			{
				rc = sqlite3PagerSync(pPager);
			}
			if (rc == SQLITE_OK)
			{
				rc = pager_end_transaction(pPager, zMaster[0] != '\0' ? 1 : 0);
				testcase(rc != SQLITE_OK);
			}
			if (rc == SQLITE_OK && zMaster[0] != '\0' && res != 0)
			{
				/* If there was a master journal and this routine will return success,
				** see if it is possible to delete the master journal.
				*/
				rc = pager_delmaster(pPager, Encoding.UTF8.GetString(zMaster, 0, zMaster.Length));
				testcase(rc != SQLITE_OK);
			}

			/* The Pager.sectorSize variable may have been updated while rolling
			** back a journal created by a process with a different sector size
			** value. Reset it to the correct value for this process.
			*/
			setSectorSize(pPager);
			return rc;
		}

		/*
		** Read the content for page pPg out of the database file and into
		** pPg.pData. A shared lock or greater must be held on the database
		** file before this function is called.
		**
		** If page 1 is read, then the value of Pager.dbFileVers[] is set to
		** the value read from the database file.
		**
		** If an IO error occurs, then the IO error is returned to the caller.
		** Otherwise, SQLITE_OK is returned.
		*/

		private static int readDbPage(PgHdr pPg)
		{
			Pager pPager = pPg.pPager;  /* Pager object associated with page pPg */
			Pgno pgno = pPg.pgno;       /* Page number to read */
			int rc = SQLITE_OK;         /* Return code */
			int isInWal = 0;            /* True if page is in log file */
			int pgsz = pPager.pageSize; /* Number of bytes to read */

			Debug.Assert(pPager.eState >= PAGER_READER &&
#if SQLITE_OMIT_MEMORYDB
0 == MEMDB
#else
 0 == pPager.memDb
#endif
);
			Debug.Assert(isOpen(pPager.fd));

			if (NEVER(!isOpen(pPager.fd)))
			{
				Debug.Assert(pPager.tempFile);
				Array.Clear(pPg.pData, 0, pPager.pageSize);// memset(pPg.pData, 0, pPager.pageSize);
				return SQLITE_OK;
			}

			if (pagerUseWal(pPager))
			{
				/* Try to pull the page from the write-ahead log. */
				rc = sqlite3WalRead(pPager.pWal, pgno, ref isInWal, pgsz, pPg.pData);
			}
			if (rc == SQLITE_OK && 0 == isInWal)
			{
				i64 iOffset = (pgno - 1) * (i64)pPager.pageSize;
				rc = sqlite3OsRead(pPager.fd, pPg.pData, pgsz, iOffset);
				if (rc == SQLITE_IOERR_SHORT_READ)
				{
					rc = SQLITE_OK;
				}
			}

			if (pgno == 1)
			{
				if (rc != 0)
				{
					/* If the read is unsuccessful, set the dbFileVers[] to something
					** that will never be a valid file version.  dbFileVers[] is a copy
					** of bytes 24..39 of the database.  Bytes 28..31 should always be
					** zero or the size of the database in page. Bytes 32..35 and 35..39
					** should be page numbers which are never 0xffffffff.  So filling
					** pPager.dbFileVers[] with all 0xff bytes should suffice.
					**
					** For an encrypted database, the situation is more complex:  bytes
					** 24..39 of the database are white noise.  But the probability of
					** white noising equaling 16 bytes of 0xff is vanishingly small so
					** we should still be ok.
					*/
					for (int i = 0; i < pPager.dbFileVers.Length; pPager.dbFileVers[i++] = 0xff)
						; // memset(pPager.dbFileVers, 0xff, sizeof(pPager.dbFileVers));
				}
				else
				{
					//u8[] dbFileVers = pPg.pData[24];
					Buffer.BlockCopy(pPg.pData, 24, pPager.dbFileVers, 0, pPager.dbFileVers.Length); //memcpy(&pPager.dbFileVers, dbFileVers, sizeof(pPager.dbFileVers));
				}
			}
			if (CODEC1(pPager, pPg.pData, pgno, SQLITE_DECRYPT))
				rc = SQLITE_NOMEM;//CODEC1(pPager, pPg.pData, pgno, 3, rc = SQLITE_NOMEM);

#if SQLITE_TEST
      //  PAGER_INCR(ref sqlite3_pager_readdb_count);
#if !TCLSH
      PAGER_INCR( ref sqlite3_pager_readdb_count );
#else
      int iValue;
      iValue = sqlite3_pager_readdb_count.iValue;
      PAGER_INCR( ref iValue );
      sqlite3_pager_readdb_count.iValue = iValue;
#endif

      PAGER_INCR( ref pPager.nRead );
#endif
			IOTRACE("PGIN %p %d\n", pPager, pgno);
			PAGERTRACE("FETCH %d page %d hash(%08x)\n",
			PAGERID(pPager), pgno, pager_pagehash(pPg));

			return rc;
		}

		/*
		** Update the value of the change-counter at offsets 24 and 92 in
		** the header and the sqlite version number at offset 96.
		**
		** This is an unconditional update.  See also the pager_incr_changecounter()
		** routine which only updates the change-counter if the update is actually
		** needed, as determined by the pPager.changeCountDone state variable.
		*/

		private static void pager_write_changecounter(PgHdr pPg)
		{
			u32 change_counter;

			/* Increment the value just read and write it back to byte 24. */
			change_counter = sqlite3Get4byte(pPg.pPager.dbFileVers, 0) + 1;
			put32bits(pPg.pData, 24, change_counter);

			/* Also store the SQLite version number in bytes 96..99 and in
			** bytes 92..95 store the change counter for which the version number
			** is valid. */
			put32bits(pPg.pData, 92, change_counter);
			put32bits(pPg.pData, 96, SQLITE_VERSION_NUMBER);
		}

#if !SQLITE_OMIT_WAL
/*
** This function is invoked once for each page that has already been
** written into the log file when a WAL transaction is rolled back.
** Parameter iPg is the page number of said page. The pCtx argument
** is actually a pointer to the Pager structure.
**
** If page iPg is present in the cache, and has no outstanding references,
** it is discarded. Otherwise, if there are one or more outstanding
** references, the page content is reloaded from the database. If the
** attempt to reload content from the database is required and fails,
** return an SQLite error code. Otherwise, SQLITE_OK.
*/
static int pagerUndoCallback(void *pCtx, Pgno iPg){
int rc = SQLITE_OK;
Pager *pPager = (Pager *)pCtx;
PgHdr *pPg;

pPg = sqlite3PagerLookup(pPager, iPg);
if( pPg ){
if( sqlite3PcachePageRefcount(pPg)==1 ){
sqlite3PcacheDrop(pPg);
}else{
rc = readDbPage(pPg);
if( rc==SQLITE_OK ){
pPager.xReiniter(pPg);
}
sqlite3PagerUnref(pPg);
}
}

/* Normally, if a transaction is rolled back, any backup processes are
** updated as data is copied out of the rollback journal and into the
** database. This is not generally possible with a WAL database, as
** rollback involves simply truncating the log file. Therefore, if one
** or more frames have already been written to the log (and therefore
** also copied into the backup databases) as part of this transaction,
** the backups must be restarted.
*/
sqlite3BackupRestart(pPager.pBackup);

return rc;
}

/*
** This function is called to rollback a transaction on a WAL database.
*/
static int pagerRollbackWal(Pager *pPager){
int rc;                         /* Return Code */
PgHdr *pList;                   /* List of dirty pages to revert */

/* For all pages in the cache that are currently dirty or have already
** been written (but not committed) to the log file, do one of the
** following:
**
**   + Discard the cached page (if refcount==0), or
**   + Reload page content from the database (if refcount>0).
*/
pPager.dbSize = pPager.dbOrigSize;
rc = sqlite3WalUndo(pPager.pWal, pagerUndoCallback, (void *)pPager);
pList = sqlite3PcacheDirtyList(pPager.pPCache);
while( pList && rc==SQLITE_OK ){
PgHdr *pNext = pList->pDirty;
rc = pagerUndoCallback((void *)pPager, pList->pgno);
pList = pNext;
}

return rc;
}

/*
** This function is a wrapper around sqlite3WalFrames(). As well as logging
** the contents of the list of pages headed by pList (connected by pDirty),
** this function notifies any active backup processes that the pages have
** changed.
**
** The list of pages passed into this routine is always sorted by page number.
** Hence, if page 1 appears anywhere on the list, it will be the first page.
*/
static int pagerWalFrames(
Pager *pPager,                  /* Pager object */
PgHdr *pList,                   /* List of frames to log */
Pgno nTruncate,                 /* Database size after this commit */
int isCommit,                   /* True if this is a commit */
int syncFlags                   /* Flags to pass to OsSync() (or 0) */
){
int rc;                         /* Return code */
#if (SQLITE_DEBUG) || (SQLITE_CHECK_PAGES)
PgHdr *p;                       /* For looping over pages */
#endif

assert( pPager.pWal );
#if SQLITE_DEBUG
/* Verify that the page list is in accending order */
for(p=pList; p && p->pDirty; p=p->pDirty){
assert( p->pgno < p->pDirty->pgno );
}
#endif

  if( isCommit ){
    /* If a WAL transaction is being committed, there is no point in writing
    ** any pages with page numbers greater than nTruncate into the WAL file.
    ** They will never be read by any client. So remove them from the pDirty
    ** list here. */
    PgHdr *p;
    PgHdr **ppNext = &pList;
    for(p=pList; (*ppNext = p); p=p->pDirty){
      if( p->pgno<=nTruncate ) ppNext = &p->pDirty;
    }
    assert( pList );
  }

if( pList->pgno==1 ) pager_write_changecounter(pList);
rc = sqlite3WalFrames(pPager.pWal,
pPager.pageSize, pList, nTruncate, isCommit, syncFlags
);
if( rc==SQLITE_OK && pPager.pBackup ){
PgHdr *p;
for(p=pList; p; p=p->pDirty){
sqlite3BackupUpdate(pPager.pBackup, p->pgno, (u8 *)p->pData);
}
}

#if SQLITE_CHECK_PAGES
pList = sqlite3PcacheDirtyList(pPager.pPCache);
for(p=pList; p; p=p->pDirty){
pager_set_pagehash(p);
}
#endif

return rc;
}

/*
** Begin a read transaction on the WAL.
**
** This routine used to be called "pagerOpenSnapshot()" because it essentially
** makes a snapshot of the database at the current point in time and preserves
** that snapshot for use by the reader in spite of concurrently changes by
** other writers or checkpointers.
*/
static int pagerBeginReadTransaction(Pager *pPager){
int rc;                         /* Return code */
int changed = 0;                /* True if cache must be reset */

assert( pagerUseWal(pPager) );
assert( pPager.eState==PAGER_OPEN || pPager.eState==PAGER_READER );

/* sqlite3WalEndReadTransaction() was not called for the previous
** transaction in locking_mode=EXCLUSIVE.  So call it now.  If we
** are in locking_mode=NORMAL and EndRead() was previously called,
** the duplicate call is harmless.
*/
sqlite3WalEndReadTransaction(pPager.pWal);

rc = sqlite3WalBeginReadTransaction(pPager.pWal, &changed);
if( rc!=SQLITE_OK || changed ){
pager_reset(pPager);
}

return rc;
}
#endif

		/*
    ** This function is called as part of the transition from PAGER_OPEN
    ** to PAGER_READER state to determine the size of the database file
    ** in pages (assuming the page size currently stored in Pager.pageSize).
    **
    ** If no error occurs, SQLITE_OK is returned and the size of the database
    ** in pages is stored in *pnPage. Otherwise, an error code (perhaps
    ** SQLITE_IOERR_FSTAT) is returned and *pnPage is left unmodified.
    */

		private static int pagerPagecount(Pager pPager, ref Pgno pnPage)
		{
			Pgno nPage;                     /* Value to return via *pnPage */

			/* Query the WAL sub-system for the database size. The WalDbsize()
			** function returns zero if the WAL is not open (i.e. Pager.pWal==0), or
			** if the database size is not available. The database size is not
			** available from the WAL sub-system if the log file is empty or
			** contains no valid committed transactions.
			*/
			Debug.Assert(pPager.eState == PAGER_OPEN);
			Debug.Assert(pPager.eLock >= SHARED_LOCK || pPager.noReadlock != 0);
			nPage = sqlite3WalDbsize(pPager.pWal);

			/* If the database size was not available from the WAL sub-system,
			** determine it based on the size of the database file. If the size
			** of the database file is not an integer multiple of the page-size,
			** round down to the nearest page. Except, any file larger than 0
			** bytes in size is considered to contain at least one page.
			*/
			if (nPage == 0)
			{
				i64 n = 0;                    /* Size of db file in bytes */
				Debug.Assert(isOpen(pPager.fd) || pPager.tempFile);
				if (isOpen(pPager.fd))
				{
					int rc = sqlite3OsFileSize(pPager.fd, ref n);
					if (rc != SQLITE_OK)
					{
						return rc;
					}
				}
				nPage = (Pgno)(n / pPager.pageSize);
				if (nPage == 0 && n > 0)
				{
					nPage = 1;
				}
			}

			/* If the current number of pages in the file is greater than the
			** configured maximum pager number, increase the allowed limit so
			** that the file can be read.
			*/
			if (nPage > pPager.mxPgno)
			{
				pPager.mxPgno = (Pgno)nPage;
			}

			pnPage = nPage;
			return SQLITE_OK;
		}

#if !SQLITE_OMIT_WAL
/*
** Check if the *-wal file that corresponds to the database opened by pPager
** exists if the database is not empy, or verify that the *-wal file does
** not exist (by deleting it) if the database file is empty.
**
** If the database is not empty and the *-wal file exists, open the pager
** in WAL mode.  If the database is empty or if no *-wal file exists and
** if no error occurs, make sure Pager.journalMode is not set to
** PAGER_JOURNALMODE_WAL.
**
** Return SQLITE_OK or an error code.
**
** The caller must hold a SHARED lock on the database file to call this
** function. Because an EXCLUSIVE lock on the db file is required to delete
** a WAL on a none-empty database, this ensures there is no race condition
** between the xAccess() below and an xDelete() being executed by some
** other connection.
*/
static int pagerOpenWalIfPresent(Pager *pPager){
int rc = SQLITE_OK;
Debug.Assert( pPager.eState==PAGER_OPEN );
Debug.Assert( pPager.eLock>=SHARED_LOCK || pPager.noReadlock );

if( !pPager.tempFile ){
int isWal;                    /* True if WAL file exists */
Pgno nPage;                   /* Size of the database file */

rc = pagerPagecount(pPager, &nPage);
if( rc ) return rc;
if( nPage==0 ){
rc = sqlite3OsDelete(pPager.pVfs, pPager.zWal, 0);
isWal = 0;
}else{
rc = sqlite3OsAccess(
pPager.pVfs, pPager.zWal, SQLITE_ACCESS_EXISTS, &isWal
);
}
if( rc==SQLITE_OK ){
if( isWal ){
testcase( sqlite3PcachePagecount(pPager.pPCache)==0 );
rc = sqlite3PagerOpenWal(pPager, 0);
}else if( pPager.journalMode==PAGER_JOURNALMODE_WAL ){
pPager.journalMode = PAGER_JOURNALMODE_DELETE;
}
}
}
return rc;
}
#endif

		/*
** Playback savepoint pSavepoint. Or, if pSavepoint==NULL, then playback
** the entire master journal file. The case pSavepoint==NULL occurs when
** a ROLLBACK TO command is invoked on a SAVEPOINT that is a transaction
** savepoint.
**
** When pSavepoint is not NULL (meaning a non-transaction savepoint is
** being rolled back), then the rollback consists of up to three stages,
** performed in the order specified:
**
**   * Pages are played back from the main journal starting at byte
**     offset PagerSavepoint.iOffset and continuing to
**     PagerSavepoint.iHdrOffset, or to the end of the main journal
**     file if PagerSavepoint.iHdrOffset is zero.
**
**   * If PagerSavepoint.iHdrOffset is not zero, then pages are played
**     back starting from the journal header immediately following
**     PagerSavepoint.iHdrOffset to the end of the main journal file.
**
**   * Pages are then played back from the sub-journal file, starting
**     with the PagerSavepoint.iSubRec and continuing to the end of
**     the journal file.
**
** Throughout the rollback process, each time a page is rolled back, the
** corresponding bit is set in a bitvec structure (variable pDone in the
** implementation below). This is used to ensure that a page is only
** rolled back the first time it is encountered in either journal.
**
** If pSavepoint is NULL, then pages are only played back from the main
** journal file. There is no need for a bitvec in this case.
**
** In either case, before playback commences the Pager.dbSize variable
** is reset to the value that it held at the start of the savepoint
** (or transaction). No page with a page-number greater than this value
** is played back. If one is encountered it is simply skipped.
*/

		private static int pagerPlaybackSavepoint(Pager pPager, PagerSavepoint pSavepoint)
		{
			i64 szJ;                 /* Effective size of the main journal */
			i64 iHdrOff;             /* End of first segment of main-journal records */
			int rc = SQLITE_OK;      /* Return code */
			Bitvec pDone = null;     /* Bitvec to ensure pages played back only once */

			Debug.Assert(pPager.eState != PAGER_ERROR);
			Debug.Assert(pPager.eState >= PAGER_WRITER_LOCKED);

			/* Allocate a bitvec to use to store the set of pages rolled back */
			if (pSavepoint != null)
			{
				pDone = sqlite3BitvecCreate(pSavepoint.nOrig);
				//if ( null == pDone )
				//{
				//  return SQLITE_NOMEM;
				//}
			}

			/* Set the database size back to the value it was before the savepoint
			** being reverted was opened.
			*/
			pPager.dbSize = pSavepoint != null ? pSavepoint.nOrig : pPager.dbOrigSize;
			pPager.changeCountDone = pPager.tempFile;

			if (!pSavepoint && pagerUseWal(pPager))
			{
				return pagerRollbackWal(pPager);
			}

			/* Use pPager.journalOff as the effective size of the main rollback
			** journal.  The actual file might be larger than this in
			** PAGER_JOURNALMODE_TRUNCATE or PAGER_JOURNALMODE_PERSIST.  But anything
			** past pPager.journalOff is off-limits to us.
			*/
			szJ = pPager.journalOff;
			Debug.Assert(pagerUseWal(pPager) == false || szJ == 0);

			/* Begin by rolling back records from the main journal starting at
			** PagerSavepoint.iOffset and continuing to the next journal header.
			** There might be records in the main journal that have a page number
			** greater than the current database size (pPager.dbSize) but those
			** will be skipped automatically.  Pages are added to pDone as they
			** are played back.
			*/
			if (pSavepoint != null && !pagerUseWal(pPager))
			{
				iHdrOff = pSavepoint.iHdrOffset != 0 ? pSavepoint.iHdrOffset : szJ;
				pPager.journalOff = pSavepoint.iOffset;
				while (rc == SQLITE_OK && pPager.journalOff < iHdrOff)
				{
					rc = pager_playback_one_page(pPager, ref pPager.journalOff, pDone, 1, 1);
				}
				Debug.Assert(rc != SQLITE_DONE);
			}
			else
			{
				pPager.journalOff = 0;
			}

			/* Continue rolling back records out of the main journal starting at
			** the first journal header seen and continuing until the effective end
			** of the main journal file.  Continue to skip out-of-range pages and
			** continue adding pages rolled back to pDone.
			*/
			while (rc == SQLITE_OK && pPager.journalOff < szJ)
			{
				u32 ii;            /* Loop counter */
				u32 nJRec;         /* Number of Journal Records */
				u32 dummy;
				rc = readJournalHdr(pPager, 0, (int)szJ, out nJRec, out dummy);
				Debug.Assert(rc != SQLITE_DONE);

				/*
				** The "pPager.journalHdr+JOURNAL_HDR_SZ(pPager)==pPager.journalOff"
				** test is related to ticket #2565.  See the discussion in the
				** pager_playback() function for additional information.
				*/
				if (nJRec == 0
				&& pPager.journalHdr + JOURNAL_HDR_SZ(pPager) >= pPager.journalOff
				)
				{
					nJRec = (u32)((szJ - pPager.journalOff) / JOURNAL_PG_SZ(pPager));
				}
				for (ii = 0; rc == SQLITE_OK && ii < nJRec && pPager.journalOff < szJ; ii++)
				{
					rc = pager_playback_one_page(pPager, ref pPager.journalOff, pDone, 1, 1);
				}
				Debug.Assert(rc != SQLITE_DONE);
			}
			Debug.Assert(rc != SQLITE_OK || pPager.journalOff >= szJ);

			/* Finally,  rollback pages from the sub-journal.  Page that were
			** previously rolled back out of the main journal (and are hence in pDone)
			** will be skipped.  Out-of-range pages are also skipped.
			*/
			if (pSavepoint != null)
			{
				u32 ii;            /* Loop counter */
				i64 offset = pSavepoint.iSubRec * (4 + pPager.pageSize);
				if (pagerUseWal(pPager))
				{
					rc = sqlite3WalSavepointUndo(pPager.pWal, pSavepoint.aWalData);
				}
				for (ii = pSavepoint.iSubRec; rc == SQLITE_OK && ii < pPager.nSubRec; ii++)
				{
					Debug.Assert(offset == ii * (4 + pPager.pageSize));
					rc = pager_playback_one_page(pPager, ref offset, pDone, 0, 1);
				}
				Debug.Assert(rc != SQLITE_DONE);
			}

			sqlite3BitvecDestroy(ref pDone);
			if (rc == SQLITE_OK)
			{
				pPager.journalOff = (int)szJ;
			}
			return rc;
		}

		/*
		** Change the maximum number of in-memory pages that are allowed.
		*/

		private static void sqlite3PagerSetCachesize(Pager pPager, int mxPage)
		{
			sqlite3PcacheSetCachesize(pPager.pPCache, mxPage);
		}

		/*
		** Adjust the robustness of the database to damage due to OS crashes
		** or power failures by changing the number of syncs()s when writing
		** the rollback journal.  There are three levels:
		**
		**    OFF       sqlite3OsSync() is never called.  This is the default
		**              for temporary and transient files.
		**
		**    NORMAL    The journal is synced once before writes begin on the
		**              database.  This is normally adequate protection, but
		**              it is theoretically possible, though very unlikely,
		**              that an inopertune power failure could leave the journal
		**              in a state which would cause damage to the database
		**              when it is rolled back.
		**
		**    FULL      The journal is synced twice before writes begin on the
		**              database (with some additional information - the nRec field
		**              of the journal header - being written in between the two
		**              syncs).  If we assume that writing a
		**              single disk sector is atomic, then this mode provides
		**              assurance that the journal will not be corrupted to the
		**              point of causing damage to the database during rollback.
		**
		** The above is for a rollback-journal mode.  For WAL mode, OFF continues
		** to mean that no syncs ever occur.  NORMAL means that the WAL is synced
		** prior to the start of checkpoint and that the database file is synced
		** at the conclusion of the checkpoint if the entire content of the WAL
		** was written back into the database.  But no sync operations occur for
		** an ordinary commit in NORMAL mode with WAL.  FULL means that the WAL
		** file is synced following each commit operation, in addition to the
		** syncs associated with NORMAL.
		**
		** Do not confuse synchronous=FULL with SQLITE_SYNC_FULL.  The
		** SQLITE_SYNC_FULL macro means to use the MacOSX-style full-fsync
		** using fcntl(F_FULLFSYNC).  SQLITE_SYNC_NORMAL means to do an
		** ordinary fsync() call.  There is no difference between SQLITE_SYNC_FULL
		** and SQLITE_SYNC_NORMAL on platforms other than MacOSX.  But the
		** synchronous=FULL versus synchronous=NORMAL setting determines when
		** the xSync primitive is called and is relevant to all platforms.
		**
		** Numeric values associated with these states are OFF==1, NORMAL=2,
		** and FULL=3.
		*/
#if !SQLITE_OMIT_PAGER_PRAGMAS

		private static void sqlite3PagerSetSafetyLevel(
		Pager pPager,         /* The pager to set safety level for */
		int level,            /* PRAGMA synchronous.  1=OFF, 2=NORMAL, 3=FULL */
		int bFullFsync,       /* PRAGMA fullfsync */
		int bCkptFullFsync    /* PRAGMA checkpoint_fullfsync */
		)
		{
			Debug.Assert(level >= 1 && level <= 3);

			pPager.noSync = (level == 1 || pPager.tempFile);
			pPager.fullSync = (level == 3 && !pPager.tempFile);
			if (pPager.noSync)
			{
				pPager.syncFlags = 0;
				pPager.ckptSyncFlags = 0;
			}
			else if (bFullFsync != 0)
			{
				pPager.syncFlags = SQLITE_SYNC_FULL;
				pPager.ckptSyncFlags = SQLITE_SYNC_FULL;
			}
			else if (bCkptFullFsync != 0)
			{
				pPager.syncFlags = SQLITE_SYNC_NORMAL;
				pPager.ckptSyncFlags = SQLITE_SYNC_FULL;
			}
			else
			{
				pPager.syncFlags = SQLITE_SYNC_NORMAL;
				pPager.ckptSyncFlags = SQLITE_SYNC_NORMAL;
			}
		}

#endif

		/*
** The following global variable is incremented whenever the library
** attempts to open a temporary file.  This information is used for
** testing and analysis only.
*/
#if SQLITE_TEST
#if !TCLSH
    static int sqlite3_opentemp_count = 0;
#else
    static tcl.lang.Var.SQLITE3_GETSET sqlite3_opentemp_count = new tcl.lang.Var.SQLITE3_GETSET( "sqlite3_opentemp_count" );
#endif
#endif

		/*
** Open a temporary file.
**
** Write the file descriptor into *pFile. Return SQLITE_OK on success
** or some other error code if we fail. The OS will automatically
** delete the temporary file when it is closed.
**
** The flags passed to the VFS layer xOpen() call are those specified
** by parameter vfsFlags ORed with the following:
**
**     SQLITE_OPEN_READWRITE
**     SQLITE_OPEN_CREATE
**     SQLITE_OPEN_EXCLUSIVE
**     SQLITE_OPEN_DELETEONCLOSE
*/

		private static int pagerOpentemp(
		Pager pPager,           /* The pager object */
		ref sqlite3_file pFile, /* Write the file descriptor here */
		int vfsFlags            /* Flags passed through to the VFS */
		)
		{
			int rc;               /* Return code */

#if SQLITE_TEST
#if !TCLSH
      sqlite3_opentemp_count++;  /* Used for testing and analysis only */
#else
      sqlite3_opentemp_count.iValue++;  /* Used for testing and analysis only */
#endif
#endif

			vfsFlags |= SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
			SQLITE_OPEN_EXCLUSIVE | SQLITE_OPEN_DELETEONCLOSE;
			int dummy = 0;
			rc = sqlite3OsOpen(pPager.pVfs, null, pFile, vfsFlags, ref dummy);
			Debug.Assert(rc != SQLITE_OK || isOpen(pFile));
			return rc;
		}

		/*
		** Set the busy handler function.
		**
		** The pager invokes the busy-handler if sqlite3OsLock() returns
		** SQLITE_BUSY when trying to upgrade from no-lock to a SHARED lock,
		** or when trying to upgrade from a RESERVED lock to an EXCLUSIVE
		** lock. It does *not* invoke the busy handler when upgrading from
		** SHARED to RESERVED, or when upgrading from SHARED to EXCLUSIVE
		** (which occurs during hot-journal rollback). Summary:
		**
		**   Transition                        | Invokes xBusyHandler
		**   --------------------------------------------------------
		**   NO_LOCK       . SHARED_LOCK      | Yes
		**   SHARED_LOCK   . RESERVED_LOCK    | No
		**   SHARED_LOCK   . EXCLUSIVE_LOCK   | No
		**   RESERVED_LOCK . EXCLUSIVE_LOCK   | Yes
		**
		** If the busy-handler callback returns non-zero, the lock is
		** retried. If it returns zero, then the SQLITE_BUSY error is
		** returned to the caller of the pager API function.
		*/

		private static void sqlite3PagerSetBusyhandler(
		Pager pPager,                         /* Pager object */
		dxBusyHandler xBusyHandler,           /* Pointer to busy-handler function */
			//int (*xBusyHandler)(void *),
		object pBusyHandlerArg                /* Argument to pass to xBusyHandler */
		)
		{
			pPager.xBusyHandler = xBusyHandler;
			pPager.pBusyHandlerArg = pBusyHandlerArg;
		}

		/*
		** Change the page size used by the Pager object. The new page size
		** is passed in *pPageSize.
		**
		** If the pager is in the error state when this function is called, it
		** is a no-op. The value returned is the error state error code (i.e.
		** one of SQLITE_IOERR, an SQLITE_IOERR_xxx sub-code or SQLITE_FULL).
		**
		** Otherwise, if all of the following are true:
		**
		**   * the new page size (value of *pPageSize) is valid (a power
		**     of two between 512 and SQLITE_MAX_PAGE_SIZE, inclusive), and
		**
		**   * there are no outstanding page references, and
		**
		**   * the database is either not an in-memory database or it is
		**     an in-memory database that currently consists of zero pages.
		**
		** then the pager object page size is set to *pPageSize.
		**
		** If the page size is changed, then this function uses sqlite3PagerMalloc()
		** to obtain a new Pager.pTmpSpace buffer. If this allocation attempt
		** fails, SQLITE_NOMEM is returned and the page size remains unchanged.
		** In all other cases, SQLITE_OK is returned.
		**
		** If the page size is not changed, either because one of the enumerated
		** conditions above is not true, the pager was in error state when this
		** function was called, or because the memory allocation attempt failed,
		** then *pPageSize is set to the old, retained page size before returning.
		*/

		private static int sqlite3PagerSetPagesize(Pager pPager, ref u32 pPageSize, int nReserve)
		{
			int rc = SQLITE_OK;
			/* It is not possible to do a full assert_pager_state() here, as this
			** function may be called from within PagerOpen(), before the state
			** of the Pager object is internally consistent.
			**
			** At one point this function returned an error if the pager was in
			** PAGER_ERROR state. But since PAGER_ERROR state guarantees that
			** there is at least one outstanding page reference, this function
			** is a no-op for that case anyhow.
			*/

			u32 pageSize = pPageSize;
			Debug.Assert(pageSize == 0 || (pageSize >= 512 && pageSize <= SQLITE_MAX_PAGE_SIZE));
			if ((pPager.memDb == 0 || pPager.dbSize == 0)
			&& sqlite3PcacheRefCount(pPager.pPCache) == 0
			&& pageSize != 0 && pageSize != (u32)pPager.pageSize
			)
			{
				//char *pNew = NULL;             /* New temp space */
				i64 nByte = 0;

				if (pPager.eState > PAGER_OPEN && isOpen(pPager.fd))
				{
					rc = sqlite3OsFileSize(pPager.fd, ref nByte);
				}
				//if ( rc == SQLITE_OK )
				//{
				//pNew = (char *)sqlite3PageMalloc(pageSize);
				//if( !pNew ) rc = SQLITE_NOMEM;
				//}
				if (rc == SQLITE_OK)
				{
					pager_reset(pPager);
					pPager.dbSize = (Pgno)(nByte / pageSize);
					pPager.pageSize = (int)pageSize;
					sqlite3PageFree(ref pPager.pTmpSpace);

					pPager.pTmpSpace = sqlite3Malloc(pageSize);// pNew;
					sqlite3PcacheSetPageSize(pPager.pPCache, (int)pageSize);
				}
			}
			pPageSize = (u32)pPager.pageSize;
			if (rc == SQLITE_OK)
			{
				if (nReserve < 0)
					nReserve = pPager.nReserve;
				Debug.Assert(nReserve >= 0 && nReserve < 1000);
				pPager.nReserve = (i16)nReserve;
				pagerReportSize(pPager);
			}
			return rc;
		}

		/*
		** Return a pointer to the "temporary page" buffer held internally
		** by the pager.  This is a buffer that is big enough to hold the
		** entire content of a database page.  This buffer is used internally
		** during rollback and will be overwritten whenever a rollback
		** occurs.  But other modules are free to use it too, as long as
		** no rollbacks are happening.
		*/

		private static byte[] sqlite3PagerTempSpace(Pager pPager)
		{
			return pPager.pTmpSpace;
		}

		/*
		** Attempt to set the maximum database page count if mxPage is positive.
		** Make no changes if mxPage is zero or negative.  And never reduce the
		** maximum page count below the current size of the database.
		**
		** Regardless of mxPage, return the current maximum page count.
		*/

		private static Pgno sqlite3PagerMaxPageCount(Pager pPager, int mxPage)
		{
			if (mxPage > 0)
			{
				pPager.mxPgno = (Pgno)mxPage;
			}
			Debug.Assert(pPager.eState != PAGER_OPEN);      /* Called only by OP_MaxPgcnt */
			Debug.Assert(pPager.mxPgno >= pPager.dbSize);  /* OP_MaxPgcnt enforces this */
			return pPager.mxPgno;
		}

		/*
		** The following set of routines are used to disable the simulated
		** I/O error mechanism.  These routines are used to avoid simulated
		** errors in places where we do not care about errors.
		**
		** Unless -DSQLITE_TEST=1 is used, these routines are all no-ops
		** and generate no code.
		*/
#if SQLITE_TEST
    //extern int sqlite3_io_error_pending;
    //extern int sqlite3_io_error_hit;
    static int saved_cnt;
    static void disable_simulated_io_errors()
    {
#if !TCLSH
      saved_cnt = sqlite3_io_error_pending;
      sqlite3_io_error_pending = -1;
#else
      saved_cnt = sqlite3_io_error_pending.iValue;
      sqlite3_io_error_pending.iValue = -1;
#endif
    }

    static void enable_simulated_io_errors()
    {
#if !TCLSH
      sqlite3_io_error_pending = saved_cnt;
#else
      sqlite3_io_error_pending.iValue = saved_cnt;
#endif
    }
#else
		//# define disable_simulated_io_errors()
		//# define enable_simulated_io_errors()
#endif

		/*
** Read the first N bytes from the beginning of the file into memory
** that pDest points to.
**
** If the pager was opened on a transient file (zFilename==""), or
** opened on a file less than N bytes in size, the output buffer is
** zeroed and SQLITE_OK returned. The rationale for this is that this
** function is used to read database headers, and a new transient or
** zero sized database has a header than consists entirely of zeroes.
**
** If any IO error apart from SQLITE_IOERR_SHORT_READ is encountered,
** the error code is returned to the caller and the contents of the
** output buffer undefined.
*/

		private static int sqlite3PagerReadFileheader(Pager pPager, int N, byte[] pDest)
		{
			int rc = SQLITE_OK;
			Array.Clear(pDest, 0, N); //memset(pDest, 0, N);
			Debug.Assert(isOpen(pPager.fd) || pPager.tempFile);

			/* This routine is only called by btree immediately after creating
			** the Pager object.  There has not been an opportunity to transition
			** to WAL mode yet.
			*/
			Debug.Assert(!pagerUseWal(pPager));

			if (isOpen(pPager.fd))
			{
				IOTRACE("DBHDR %p 0 %d\n", pPager, N);
				rc = sqlite3OsRead(pPager.fd, pDest, N, 0);
				if (rc == SQLITE_IOERR_SHORT_READ)
				{
					rc = SQLITE_OK;
				}
			}
			return rc;
		}

		/*
		** This function may only be called when a read-transaction is open on
		** the pager. It returns the total number of pages in the database.
		**
		** However, if the file is between 1 and <page-size> bytes in size, then
		** this is considered a 1 page file.
		*/

		private static void sqlite3PagerPagecount(Pager pPager, out Pgno pnPage)
		{
			Debug.Assert(pPager.eState >= PAGER_READER);
			Debug.Assert(pPager.eState != PAGER_WRITER_FINISHED);
			pnPage = pPager.dbSize;
		}

		/*
		** Try to obtain a lock of type locktype on the database file. If
		** a similar or greater lock is already held, this function is a no-op
		** (returning SQLITE_OK immediately).
		**
		** Otherwise, attempt to obtain the lock using sqlite3OsLock(). Invoke
		** the busy callback if the lock is currently not available. Repeat
		** until the busy callback returns false or until the attempt to
		** obtain the lock succeeds.
		**
		** Return SQLITE_OK on success and an error code if we cannot obtain
		** the lock. If the lock is obtained successfully, set the Pager.state
		** variable to locktype before returning.
		*/

		private static int pager_wait_on_lock(Pager pPager, int locktype)
		{
			int rc;                              /* Return code */

			/* Check that this is either a no-op (because the requested lock is
			** already held, or one of the transistions that the busy-handler
			** may be invoked during, according to the comment above
			** sqlite3PagerSetBusyhandler().
			*/
			Debug.Assert((pPager.eLock >= locktype)
			|| (pPager.eLock == NO_LOCK && locktype == SHARED_LOCK)
			|| (pPager.eLock == RESERVED_LOCK && locktype == EXCLUSIVE_LOCK)
			);

			do
			{
				rc = pagerLockDb(pPager, locktype);
			} while (rc == SQLITE_BUSY && pPager.xBusyHandler(pPager.pBusyHandlerArg) != 0);
			return rc;
		}

		/*
		** Function assertTruncateConstraint(pPager) checks that one of the
		** following is true for all dirty pages currently in the page-cache:
		**
		**   a) The page number is less than or equal to the size of the
		**      current database image, in pages, OR
		**
		**   b) if the page content were written at this time, it would not
		**      be necessary to write the current content out to the sub-journal
		**      (as determined by function subjRequiresPage()).
		**
		** If the condition asserted by this function were not true, and the
		** dirty page were to be discarded from the cache via the pagerStress()
		** routine, pagerStress() would not write the current page content to
		** the database file. If a savepoint transaction were rolled back after
		** this happened, the correct behaviour would be to restore the current
		** content of the page. However, since this content is not present in either
		** the database file or the portion of the rollback journal and
		** sub-journal rolled back the content could not be restored and the
		** database image would become corrupt. It is therefore fortunate that
		** this circumstance cannot arise.
		*/
#if SQLITE_DEBUG

		private static void assertTruncateConstraintCb(PgHdr pPg)
		{
			Debug.Assert((pPg.flags & PGHDR_DIRTY) != 0);
			Debug.Assert(!subjRequiresPage(pPg) || pPg.pgno <= pPg.pPager.dbSize);
		}

		private static void assertTruncateConstraint(Pager pPager)
		{
			sqlite3PcacheIterateDirty(pPager.pPCache, assertTruncateConstraintCb);
		}

#else
//# define assertTruncateConstraint(pPager)
static void assertTruncateConstraintCb(PgHdr pPg) { }
static void assertTruncateConstraint(Pager pPager) { }
#endif

		/*
** Truncate the in-memory database file image to nPage pages. This
** function does not actually modify the database file on disk. It
** just sets the internal state of the pager object so that the
** truncation will be done when the current transaction is committed.
*/

		private static void sqlite3PagerTruncateImage(Pager pPager, u32 nPage)
		{
			Debug.Assert(pPager.dbSize >= nPage);
			Debug.Assert(pPager.eState >= PAGER_WRITER_CACHEMOD);
			pPager.dbSize = nPage;
			assertTruncateConstraint(pPager);
		}

		/*
		** This function is called before attempting a hot-journal rollback. It
		** syncs the journal file to disk, then sets pPager.journalHdr to the
		** size of the journal file so that the pager_playback() routine knows
		** that the entire journal file has been synced.
		**
		** Syncing a hot-journal to disk before attempting to roll it back ensures
		** that if a power-failure occurs during the rollback, the process that
		** attempts rollback following system recovery sees the same journal
		** content as this process.
		**
		** If everything goes as planned, SQLITE_OK is returned. Otherwise,
		** an SQLite error code.
		*/

		private static int pagerSyncHotJournal(Pager pPager)
		{
			int rc = SQLITE_OK;
			if (!pPager.noSync)
			{
				rc = sqlite3OsSync(pPager.jfd, SQLITE_SYNC_NORMAL);
			}
			if (rc == SQLITE_OK)
			{
				rc = sqlite3OsFileSize(pPager.jfd, ref pPager.journalHdr);
			}
			return rc;
		}

		/*
		** Shutdown the page cache.  Free all memory and close all files.
		**
		** If a transaction was in progress when this routine is called, that
		** transaction is rolled back.  All outstanding pages are invalidated
		** and their memory is freed.  Any attempt to use a page associated
		** with this page cache after this function returns will likely
		** result in a coredump.
		**
		** This function always succeeds. If a transaction is active an attempt
		** is made to roll it back. If an error occurs during the rollback
		** a hot journal may be left in the filesystem but no error is returned
		** to the caller.
		*/

		private static int sqlite3PagerClose(Pager pPager)
		{
#if SQLITE_TEST
      disable_simulated_io_errors();
#endif
			sqlite3BeginBenignMalloc();
			/* pPager.errCode = 0; */
			pPager.exclusiveMode = false;
#if !SQLITE_OMIT_WAL
      u8[] pTmp = pPager.pTmpSpace;
      sqlite3WalClose(pPager->pWal, pPager->ckptSyncFlags, pPager->pageSize, pTmp);
      pPager.pWal = 0;
#endif
			pager_reset(pPager);
#if SQLITE_OMIT_MEMORYDB
      if ( 1 == MEMDB )
#else
			if (1 == pPager.memDb)
#endif
			{
				pager_unlock(pPager);
			}
			else
			{
				/* If it is open, sync the journal file before calling UnlockAndRollback.
				** If this is not done, then an unsynced portion of the open journal
				** file may be played back into the database. If a power failure occurs
				** while this is happening, the database could become corrupt.
				**
				** If an error occurs while trying to sync the journal, shift the pager
				** into the ERROR state. This causes UnlockAndRollback to unlock the
				** database and close the journal file without attempting to roll it
				** back or finalize it. The next database user will have to do hot-journal
				** rollback before accessing the database file.
				*/
				if (isOpen(pPager.jfd))
				{
					pager_error(pPager, pagerSyncHotJournal(pPager));
				}
				pagerUnlockAndRollback(pPager);
			}
			sqlite3EndBenignMalloc();
#if SQLITE_TEST
      enable_simulated_io_errors();
#endif

			PAGERTRACE("CLOSE %d\n", PAGERID(pPager));
			IOTRACE("CLOSE %p\n", pPager);
			sqlite3OsClose(pPager.jfd);
			sqlite3OsClose(pPager.fd);
			//sqlite3_free( ref pTmp );
			sqlite3PcacheClose(pPager.pPCache);

#if SQLITE_HAS_CODEC
			if (pPager.xCodecFree != null)
				pPager.xCodecFree(ref pPager.pCodec);
#endif
			Debug.Assert(null == pPager.aSavepoint && !pPager.pInJournal);
			Debug.Assert(!isOpen(pPager.jfd) && !isOpen(pPager.sjfd));

			//sqlite3_free( ref pPager );
			return SQLITE_OK;
		}

#if !NDEBUG || SQLITE_TEST
		/*
** Return the page number for page pPg.
*/

		private static Pgno sqlite3PagerPagenumber(DbPage pPg)
		{
			return pPg.pgno;
		}

#else
static Pgno sqlite3PagerPagenumber( DbPage pPg )    {      return pPg.pgno;    }
#endif

		/*
** Increment the reference count for page pPg.
*/

		private static void sqlite3PagerRef(DbPage pPg)
		{
			sqlite3PcacheRef(pPg);
		}

		/*
		** Sync the journal. In other words, make sure all the pages that have
		** been written to the journal have actually reached the surface of the
		** disk and can be restored in the event of a hot-journal rollback.
		**
		** If the Pager.noSync flag is set, then this function is a no-op.
		** Otherwise, the actions required depend on the journal-mode and the
		** device characteristics of the the file-system, as follows:
		**
		**   * If the journal file is an in-memory journal file, no action need
		**     be taken.
		**
		**   * Otherwise, if the device does not support the SAFE_APPEND property,
		**     then the nRec field of the most recently written journal header
		**     is updated to contain the number of journal records that have
		**     been written following it. If the pager is operating in full-sync
		**     mode, then the journal file is synced before this field is updated.
		**
		**   * If the device does not support the SEQUENTIAL property, then
		**     journal file is synced.
		**
		** Or, in pseudo-code:
		**
		**   if( NOT <in-memory journal> ){
		**     if( NOT SAFE_APPEND ){
		**       if( <full-sync mode> ) xSync(<journal file>);
		**       <update nRec field>
		**     }
		**     if( NOT SEQUENTIAL ) xSync(<journal file>);
		**   }
		**
		** If successful, this routine clears the PGHDR_NEED_SYNC flag of every
		** page currently held in memory before returning SQLITE_OK. If an IO
		** error is encountered, then the IO error code is returned to the caller.
		*/

		private static int syncJournal(Pager pPager, int newHdr)
		{
			int rc = SQLITE_OK;
			Debug.Assert(pPager.eState == PAGER_WRITER_CACHEMOD
			|| pPager.eState == PAGER_WRITER_DBMOD
			);
			Debug.Assert(assert_pager_state(pPager));
			Debug.Assert(!pagerUseWal(pPager));

			rc = sqlite3PagerExclusiveLock(pPager);
			if (rc != SQLITE_OK)
				return rc;

			if (!pPager.noSync)
			{
				Debug.Assert(!pPager.tempFile);
				if (isOpen(pPager.jfd) && pPager.journalMode != PAGER_JOURNALMODE_MEMORY)
				{
					int iDc = sqlite3OsDeviceCharacteristics(pPager.fd);
					Debug.Assert(isOpen(pPager.jfd));

					if (0 == (iDc & SQLITE_IOCAP_SAFE_APPEND))
					{
						/* This block deals with an obscure problem. If the last connection
						** that wrote to this database was operating in persistent-journal
						** mode, then the journal file may at this point actually be larger
						** than Pager.journalOff bytes. If the next thing in the journal
						** file happens to be a journal-header (written as part of the
						** previous connection's transaction), and a crash or power-failure
						** occurs after nRec is updated but before this connection writes
						** anything else to the journal file (or commits/rolls back its
						** transaction), then SQLite may become confused when doing the
						** hot-journal rollback following recovery. It may roll back all
						** of this connections data, then proceed to rolling back the old,
						** out-of-date data that follows it. Database corruption.
						**
						** To work around this, if the journal file does appear to contain
						** a valid header following Pager.journalOff, then write a 0x00
						** byte to the start of it to prevent it from being recognized.
						**
						** Variable iNextHdrOffset is set to the offset at which this
						** problematic header will occur, if it exists. aMagic is used
						** as a temporary buffer to inspect the first couple of bytes of
						** the potential journal header.
						*/
						i64 iNextHdrOffset;
						u8[] aMagic = new u8[8];
						u8[] zHeader = new u8[aJournalMagic.Length + 4];
						aJournalMagic.CopyTo(zHeader, 0);// memcpy(zHeader, aJournalMagic, sizeof(aJournalMagic));
						put32bits(zHeader, aJournalMagic.Length, pPager.nRec);
						iNextHdrOffset = journalHdrOffset(pPager);
						rc = sqlite3OsRead(pPager.jfd, aMagic, 8, iNextHdrOffset);
						if (rc == SQLITE_OK && 0 == memcmp(aMagic, aJournalMagic, 8))
						{
							u8[] zerobyte = new u8[1];
							rc = sqlite3OsWrite(pPager.jfd, zerobyte, 1, iNextHdrOffset);
						}
						if (rc != SQLITE_OK && rc != SQLITE_IOERR_SHORT_READ)
						{
							return rc;
						}

						/* Write the nRec value into the journal file header. If in
						** full-synchronous mode, sync the journal first. This ensures that
						** all data has really hit the disk before nRec is updated to mark
						** it as a candidate for rollback.
						**
						** This is not required if the persistent media supports the
						** SAFE_APPEND property. Because in this case it is not possible
						** for garbage data to be appended to the file, the nRec field
						** is populated with 0xFFFFFFFF when the journal header is written
						** and never needs to be updated.
						*/
						if (pPager.fullSync && 0 == (iDc & SQLITE_IOCAP_SEQUENTIAL))
						{
							PAGERTRACE("SYNC journal of %d\n", PAGERID(pPager));
							IOTRACE("JSYNC %p\n", pPager);
							rc = sqlite3OsSync(pPager.jfd, pPager.syncFlags);
							if (rc != SQLITE_OK)
								return rc;
						}
						IOTRACE("JHDR %p %lld\n", pPager, pPager.journalHdr);
						rc = sqlite3OsWrite(
						pPager.jfd, zHeader, zHeader.Length, pPager.journalHdr
						);
						if (rc != SQLITE_OK)
							return rc;
					}
					if (0 == (iDc & SQLITE_IOCAP_SEQUENTIAL))
					{
						PAGERTRACE("SYNC journal of %d\n", PAGERID(pPager));
						IOTRACE("JSYNC %p\n", pPager);
						rc = sqlite3OsSync(pPager.jfd, pPager.syncFlags |
						(pPager.syncFlags == SQLITE_SYNC_FULL ? SQLITE_SYNC_DATAONLY : 0)
						);
						if (rc != SQLITE_OK)
							return rc;
					}
					pPager.journalHdr = pPager.journalOff;
					if (newHdr != 0 && 0 == (iDc & SQLITE_IOCAP_SAFE_APPEND))
					{
						pPager.nRec = 0;
						rc = writeJournalHdr(pPager);
						if (rc != SQLITE_OK)
							return rc;
					}
				}
				else
				{
					pPager.journalHdr = pPager.journalOff;
				}
			}
			/* Unless the pager is in noSync mode, the journal file was just
			** successfully synced. Either way, clear the PGHDR_NEED_SYNC flag on
			** all pages.
			*/
			sqlite3PcacheClearSyncFlags(pPager.pPCache);
			pPager.eState = PAGER_WRITER_DBMOD;
			Debug.Assert(assert_pager_state(pPager));
			return SQLITE_OK;
		}

		/*
		** The argument is the first in a linked list of dirty pages connected
		** by the PgHdr.pDirty pointer. This function writes each one of the
		** in-memory pages in the list to the database file. The argument may
		** be NULL, representing an empty list. In this case this function is
		** a no-op.
		**
		** The pager must hold at least a RESERVED lock when this function
		** is called. Before writing anything to the database file, this lock
		** is upgraded to an EXCLUSIVE lock. If the lock cannot be obtained,
		** SQLITE_BUSY is returned and no data is written to the database file.
		**
		** If the pager is a temp-file pager and the actual file-system file
		** is not yet open, it is created and opened before any data is
		** written out.
		**
		** Once the lock has been upgraded and, if necessary, the file opened,
		** the pages are written out to the database file in list order. Writing
		** a page is skipped if it meets either of the following criteria:
		**
		**   * The page number is greater than Pager.dbSize, or
		**   * The PGHDR_DONT_WRITE flag is set on the page.
		**
		** If writing out a page causes the database file to grow, Pager.dbFileSize
		** is updated accordingly. If page 1 is written out, then the value cached
		** in Pager.dbFileVers[] is updated to match the new value stored in
		** the database file.
		**
		** If everything is successful, SQLITE_OK is returned. If an IO error
		** occurs, an IO error code is returned. Or, if the EXCLUSIVE lock cannot
		** be obtained, SQLITE_BUSY is returned.
		*/

		private static int pager_write_pagelist(Pager pPager, PgHdr pList)
		{
			int rc = SQLITE_OK;                  /* Return code */

			/* This function is only called for rollback pagers in WRITER_DBMOD state. */
			Debug.Assert(!pagerUseWal(pPager));
			Debug.Assert(pPager.eState == PAGER_WRITER_DBMOD);
			Debug.Assert(pPager.eLock == EXCLUSIVE_LOCK);
			/* If the file is a temp-file has not yet been opened, open it now. It
			** is not possible for rc to be other than SQLITE_OK if this branch
			** is taken, as pager_wait_on_lock() is a no-op for temp-files.
			*/
			if (!isOpen(pPager.fd))
			{
				Debug.Assert(pPager.tempFile && rc == SQLITE_OK);
				rc = pagerOpentemp(pPager, ref pPager.fd, (int)pPager.vfsFlags);
			}

			/* Before the first write, give the VFS a hint of what the final
			** file size will be.
			*/
			Debug.Assert(rc != SQLITE_OK || isOpen(pPager.fd));
			if (rc == SQLITE_OK && pPager.dbSize > pPager.dbHintSize)
			{
				sqlite3_int64 szFile = pPager.pageSize * (sqlite3_int64)pPager.dbSize;
				sqlite3OsFileControl(pPager.fd, SQLITE_FCNTL_SIZE_HINT, ref szFile);
				pPager.dbHintSize = pPager.dbSize;
			}
			while (rc == SQLITE_OK && pList)
			{
				Pgno pgno = pList.pgno;

				/* If there are dirty pages in the page cache with page numbers greater
				** than Pager.dbSize, this means sqlite3PagerTruncateImage() was called to
				** make the file smaller (presumably by auto-vacuum code). Do not write
				** any such pages to the file.
				**
				** Also, do not write out any page that has the PGHDR_DONT_WRITE flag
				** set (set by sqlite3PagerDontWrite()).
				*/
				if (pList.pgno <= pPager.dbSize && 0 == (pList.flags & PGHDR_DONT_WRITE))
				{
					i64 offset = (pList.pgno - 1) * (i64)pPager.pageSize;      /* Offset to write */
					byte[] pData = null;                                   /* Data to write */

					Debug.Assert((pList.flags & PGHDR_NEED_SYNC) == 0);
					if (pList.pgno == 1)
						pager_write_changecounter(pList);

					/* Encode the database */
					if (CODEC2(pPager, pList.pData, pgno, SQLITE_ENCRYPT_WRITE_CTX, ref pData))
						return SQLITE_NOMEM;//     CODEC2(pPager, pList.pData, pgno, 6, return SQLITE_NOMEM, pData);

					/* Write out the page data. */
					rc = sqlite3OsWrite(pPager.fd, pData, pPager.pageSize, offset);
					/* If page 1 was just written, update Pager.dbFileVers to match
					** the value now stored in the database file. If writing this
					** page caused the database file to grow, update dbFileSize.
					*/
					if (pgno == 1)
					{
						Buffer.BlockCopy(pData, 24, pPager.dbFileVers, 0, pPager.dbFileVers.Length);// memcpy(pPager.dbFileVers, pData[24], pPager.dbFileVers).Length;
					}
					if (pgno > pPager.dbFileSize)
					{
						pPager.dbFileSize = pgno;
					}
					/* Update any backup objects copying the contents of this pager. */
					sqlite3BackupUpdate(pPager.pBackup, pgno, pList.pData);

					PAGERTRACE("STORE %d page %d hash(%08x)\n",
					PAGERID(pPager), pgno, pager_pagehash(pList));
					IOTRACE("PGOUT %p %d\n", pPager, pgno);
#if SQLITE_TEST
#if !TCLSH
          PAGER_INCR( ref sqlite3_pager_writedb_count );
#else
          int iValue;
          iValue = sqlite3_pager_writedb_count.iValue;
          PAGER_INCR( ref iValue );
          sqlite3_pager_writedb_count.iValue = iValue;
#endif

          PAGER_INCR( ref pPager.nWrite );
#endif
				}
				else
				{
					PAGERTRACE("NOSTORE %d page %d\n", PAGERID(pPager), pgno);
				}
				pager_set_pagehash(pList);
				pList = pList.pDirty;
			}
			return rc;
		}

		/*
		** Ensure that the sub-journal file is open. If it is already open, this
		** function is a no-op.
		**
		** SQLITE_OK is returned if everything goes according to plan. An
		** SQLITE_IOERR_XXX error code is returned if a call to sqlite3OsOpen()
		** fails.
		*/

		private static int openSubJournal(Pager pPager)
		{
			int rc = SQLITE_OK;
			if (!isOpen(pPager.sjfd))
			{
				if (pPager.journalMode == PAGER_JOURNALMODE_MEMORY || pPager.subjInMemory != 0)
				{
					sqlite3MemJournalOpen(pPager.sjfd);
				}
				else
				{
					rc = pagerOpentemp(pPager, ref pPager.sjfd, SQLITE_OPEN_SUBJOURNAL);
				}
			}
			return rc;
		}

		/*
		** Append a record of the current state of page pPg to the sub-journal.
		** It is the callers responsibility to use subjRequiresPage() to check
		** that it is really required before calling this function.
		**
		** If successful, set the bit corresponding to pPg.pgno in the bitvecs
		** for all open savepoints before returning.
		**
		** This function returns SQLITE_OK if everything is successful, an IO
		** error code if the attempt to write to the sub-journal fails, or
		** SQLITE_NOMEM if a malloc fails while setting a bit in a savepoint
		** bitvec.
		*/

		private static int subjournalPage(PgHdr pPg)
		{
			int rc = SQLITE_OK;
			Pager pPager = pPg.pPager;
			if (pPager.journalMode != PAGER_JOURNALMODE_OFF)
			{
				/* Open the sub-journal, if it has not already been opened */
				Debug.Assert(pPager.useJournal != 0);
				Debug.Assert(isOpen(pPager.jfd) || pagerUseWal(pPager));
				Debug.Assert(isOpen(pPager.sjfd) || pPager.nSubRec == 0);
				Debug.Assert(pagerUseWal(pPager)
				|| pageInJournal(pPg)
				|| pPg.pgno > pPager.dbOrigSize
				);
				rc = openSubJournal(pPager);

				/* If the sub-journal was opened successfully (or was already open),
				** write the journal record into the file.  */
				if (rc == SQLITE_OK)
				{
					byte[] pData = pPg.pData;
					i64 offset = pPager.nSubRec * (4 + pPager.pageSize);
					byte[] pData2 = null;

					if (CODEC2(pPager, pData, pPg.pgno, SQLITE_ENCRYPT_READ_CTX, ref pData2))
						return SQLITE_NOMEM;//CODEC2(pPager, pData, pPg.pgno, 7, return SQLITE_NOMEM, pData2);
					PAGERTRACE("STMT-JOURNAL %d page %d\n", PAGERID(pPager), pPg.pgno);
					rc = write32bits(pPager.sjfd, offset, pPg.pgno);
					if (rc == SQLITE_OK)
					{
						rc = sqlite3OsWrite(pPager.sjfd, pData2, pPager.pageSize, offset + 4);
					}
				}
			}
			if (rc == SQLITE_OK)
			{
				pPager.nSubRec++;
				Debug.Assert(pPager.nSavepoint > 0);
				rc = addToSavepointBitvecs(pPager, pPg.pgno);
			}
			return rc;
		}

		/*
		** This function is called by the pcache layer when it has reached some
		** soft memory limit. The first argument is a pointer to a Pager object
		** (cast as a void*). The pager is always 'purgeable' (not an in-memory
		** database). The second argument is a reference to a page that is
		** currently dirty but has no outstanding references. The page
		** is always associated with the Pager object passed as the first
		** argument.
		**
		** The job of this function is to make pPg clean by writing its contents
		** out to the database file, if possible. This may involve syncing the
		** journal file.
		**
		** If successful, sqlite3PcacheMakeClean() is called on the page and
		** SQLITE_OK returned. If an IO error occurs while trying to make the
		** page clean, the IO error code is returned. If the page cannot be
		** made clean for some other reason, but no error occurs, then SQLITE_OK
		** is returned by sqlite3PcacheMakeClean() is not called.
		*/

		private static int pagerStress(object p, PgHdr pPg)
		{
			Pager pPager = (Pager)p;
			int rc = SQLITE_OK;

			Debug.Assert(pPg.pPager == pPager);
			Debug.Assert((pPg.flags & PGHDR_DIRTY) != 0);

			/* The doNotSyncSpill flag is set during times when doing a sync of
			** journal (and adding a new header) is not allowed.  This occurs
			** during calls to sqlite3PagerWrite() while trying to journal multiple
			** pages belonging to the same sector.
			**
			** The doNotSpill flag inhibits all cache spilling regardless of whether
			** or not a sync is required.  This is set during a rollback.
			**
			** Spilling is also prohibited when in an error state since that could
			** lead to database corruption.   In the current implementaton it
			** is impossible for sqlite3PCacheFetch() to be called with createFlag==1
			** while in the error state, hence it is impossible for this routine to
			** be called in the error state.  Nevertheless, we include a NEVER()
			** test for the error state as a safeguard against future changes.
			*/
			if (NEVER(pPager.errCode != 0))
				return SQLITE_OK;
			if (pPager.doNotSpill != 0)
				return SQLITE_OK;
			if (pPager.doNotSyncSpill != 0 && (pPg.flags & PGHDR_NEED_SYNC) != 0)
			{
				return SQLITE_OK;
			}
			pPg.pDirty = null;
			if (pagerUseWal(pPager))
			{
				/* Write a single frame for this page to the log. */
				if (subjRequiresPage(pPg))
				{
					rc = subjournalPage(pPg);
				}
				if (rc == SQLITE_OK)
				{
					rc = pagerWalFrames(pPager, pPg, 0, 0, 0);
				}
			}
			else
			{
				/* Sync the journal file if required. */
				if ((pPg.flags & PGHDR_NEED_SYNC) != 0
				|| pPager.eState == PAGER_WRITER_CACHEMOD
				)
				{
					rc = syncJournal(pPager, 1);
				}

				/* If the page number of this page is larger than the current size of
				** the database image, it may need to be written to the sub-journal.
				** This is because the call to pager_write_pagelist() below will not
				** actually write data to the file in this case.
				**
				** Consider the following sequence of events:
				**
				**   BEGIN;
				**     <journal page X>
				**     <modify page X>
				**     SAVEPOINT sp;
				**       <shrink database file to Y pages>
				**       pagerStress(page X)
				**     ROLLBACK TO sp;
				**
				** If (X>Y), then when pagerStress is called page X will not be written
				** out to the database file, but will be dropped from the cache. Then,
				** following the "ROLLBACK TO sp" statement, reading page X will read
				** data from the database file. This will be the copy of page X as it
				** was when the transaction started, not as it was when "SAVEPOINT sp"
				** was executed.
				**
				** The solution is to write the current data for page X into the
				** sub-journal file now (if it is not already there), so that it will
				** be restored to its current value when the "ROLLBACK TO sp" is
				** executed.
				*/
				if (NEVER(
				rc == SQLITE_OK && pPg.pgno > pPager.dbSize && subjRequiresPage(pPg)
				))
				{
					rc = subjournalPage(pPg);
				}

				/* Write the contents of the page out to the database file. */
				if (rc == SQLITE_OK)
				{
					Debug.Assert((pPg.flags & PGHDR_NEED_SYNC) == 0);
					rc = pager_write_pagelist(pPager, pPg);
				}
			}
			/* Mark the page as clean. */
			if (rc == SQLITE_OK)
			{
				PAGERTRACE("STRESS %d page %d\n", PAGERID(pPager), pPg.pgno);
				sqlite3PcacheMakeClean(pPg);
			}

			return pager_error(pPager, rc);
		}

		/*
		** Allocate and initialize a new Pager object and put a pointer to it
		** in *ppPager. The pager should eventually be freed by passing it
		** to sqlite3PagerClose().
		**
		** The zFilename argument is the path to the database file to open.
		** If zFilename is NULL then a randomly-named temporary file is created
		** and used as the file to be cached. Temporary files are be deleted
		** automatically when they are closed. If zFilename is ":memory:" then
		** all information is held in cache. It is never written to disk.
		** This can be used to implement an in-memory database.
		**
		** The nExtra parameter specifies the number of bytes of space allocated
		** along with each page reference. This space is available to the user
		** via the sqlite3PagerGetExtra() API.
		**
		** The flags argument is used to specify properties that affect the
		** operation of the pager. It should be passed some bitwise combination
		** of the PAGER_OMIT_JOURNAL and PAGER_NO_READLOCK flags.
		**
		** The vfsFlags parameter is a bitmask to pass to the flags parameter
		** of the xOpen() method of the supplied VFS when opening files.
		**
		** If the pager object is allocated and the specified file opened
		** successfully, SQLITE_OK is returned and *ppPager set to point to
		** the new pager object. If an error occurs, *ppPager is set to NULL
		** and error code returned. This function may return SQLITE_NOMEM
		** (sqlite3Malloc() is used to allocate memory), SQLITE_CANTOPEN or
		** various SQLITE_IO_XXX errors.
		*/

		private static int sqlite3PagerOpen(
		sqlite3_vfs pVfs,        /* The virtual file system to use */
		out Pager ppPager,       /* OUT: Return the Pager structure here */
		string zFilename,        /* Name of the database file to open */
		int nExtra,              /* Extra bytes append to each in-memory page */
		int flags,               /* flags controlling this file */
		int vfsFlags,            /* flags passed through to sqlite3_vfs.xOpen() */
		dxReiniter xReinit       /* Function to reinitialize pages */
		)
		{
			u8 pPtr;
			Pager pPager = null;     /* Pager object to allocate and return */
			int rc = SQLITE_OK;      /* Return code */
			u8 tempFile = 0;         /* True for temp files (incl. in-memory files) */ // Needs to be u8 for later tests
			u8 memDb = 0;            /* True if this is an in-memory file */
			bool readOnly = false;   /* True if this is a read-only file */
			int journalFileSize;     /* Bytes to allocate for each journal fd */
			StringBuilder zPathname = null; /* Full path to database file */
			int nPathname = 0;       /* Number of bytes in zPathname */
			bool useJournal = (flags & PAGER_OMIT_JOURNAL) == 0; /* False to omit journal */
			bool noReadlock = (flags & PAGER_NO_READLOCK) != 0;  /* True to omit read-lock */
			int pcacheSize = sqlite3PcacheSize();       /* Bytes to allocate for PCache */
			u32 szPageDflt = SQLITE_DEFAULT_PAGE_SIZE;  /* Default page size */
			string zUri = null;     /* URI args to copy */
			int nUri = 0;           /* Number of bytes of URI args at *zUri */

			/* Figure out how much space is required for each journal file-handle
			** (there are two of them, the main journal and the sub-journal). This
			** is the maximum space required for an in-memory journal file handle
			** and a regular journal file-handle. Note that a "regular journal-handle"
			** may be a wrapper capable of caching the first portion of the journal
			** file in memory to implement the atomic-write optimization (see
			** source file journal.c).
			*/
			if (sqlite3JournalSize(pVfs) > sqlite3MemJournalSize())
			{
				journalFileSize = ROUND8(sqlite3JournalSize(pVfs));
			}
			else
			{
				journalFileSize = ROUND8(sqlite3MemJournalSize());
			}

			/* Set the output variable to NULL in case an error occurs. */
			ppPager = null;

#if !SQLITE_OMIT_MEMORYDB
			if ((flags & PAGER_MEMORY) != 0)
			{
				memDb = 1;
				zFilename = null;
			}
#endif

			/* Compute and store the full pathname in an allocated buffer pointed
      ** to by zPathname, length nPathname. Or, if this is a temporary file,
      ** leave both nPathname and zPathname set to 0.
      */
			if (!String.IsNullOrEmpty(zFilename))
			{
				nPathname = pVfs.mxPathname + 1;
				zPathname = new StringBuilder(nPathname * 2);// sqlite3Malloc( nPathname * 2 );
				//if ( zPathname == null )
				//{
				//  return SQLITE_NOMEM;
				//}
				//zPathname[0] = 0; /* Make sure initialized even if FullPathname() fails */
				rc = sqlite3OsFullPathname(pVfs, zFilename, nPathname, zPathname);

				nPathname = sqlite3Strlen30(zPathname);
				zUri = zFilename;
				//string z = zUri = zFilename;//.Substring(sqlite3Strlen30( zFilename ) );
				//while ( *z )
				//{
				//  z += sqlite3Strlen30( z ) + 1;
				//  z += sqlite3Strlen30( z ) + 1;
				//}
				//nUri = zUri.Length;//        &z[1] - zUri;
				if (rc == SQLITE_OK && nPathname + 8 > pVfs.mxPathname)
				{
					/* This branch is taken when the journal path required by
					** the database being opened will be more than pVfs.mxPathname
					** bytes in length. This means the database cannot be opened,
					** as it will not be possible to open the journal file or even
					** check for a hot-journal before reading.
					*/
					rc = SQLITE_CANTOPEN_BKPT();
				}
				if (rc != SQLITE_OK)
				{
					//sqlite3_free( ref zPathname );
					return rc;
				}
			}

			/* Allocate memory for the Pager structure, PCache object, the
			** three file descriptors, the database file name and the journal
			** file name. The layout in memory is as follows:
			**
			**     Pager object                    (sizeof(Pager) bytes)
			**     PCache object                   (sqlite3PcacheSize() bytes)
			**     Database file handle            (pVfs.szOsFile bytes)
			**     Sub-journal file handle         (journalFileSize bytes)
			**     Main journal file handle        (journalFileSize bytes)
			**     Database file name              (nPathname+1 bytes)
			**     Journal file name               (nPathname+8+1 bytes)
			*/
			//pPtr = (u8 *)sqlite3MallocZero(
			//  ROUND8(sizeof(*pPager)) +           /* Pager structure */
			//  ROUND8(pcacheSize)      +           /* PCache object */
			//  ROUND8(pVfs.szOsFile)   +           /* The main db file */
			//  journalFileSize * 2 +       /* The two journal files */
			//  nPathname + 1 + nUri +         /* zFilename */
			//  nPathname + 8 + 1           /* zJournal */
			//#if !SQLITE_OMIT_WAL
			//    + nPathname + 4 + 1              /* zWal */
			//#endif
			//);
			//  Debug.Assert( EIGHT_BYTE_ALIGNMENT(SQLITE_INT_TO_PTR(journalFileSize)));
			//if( !pPtr ){
			//  //sqlite3_free(zPathname);
			//  return SQLITE_NOMEM;
			//}
			pPager = new Pager();//(Pager*)(pPtr);
			pPager.pPCache = new PCache();//(PCache*)(pPtr += ROUND8(sizeof(*pPager)));
			pPager.fd = new sqlite3_file();//(sqlite3_file*)(pPtr += ROUND8(pcacheSize));
			pPager.sjfd = new sqlite3_file();//(sqlite3_file*)(pPtr += ROUND8(pVfs.szOsFile));
			pPager.jfd = new sqlite3_file();//(sqlite3_file*)(pPtr += journalFileSize);
			//pPager.zFilename =    (char*)(pPtr += journalFileSize);
			//Debug.Assert( EIGHT_BYTE_ALIGNMENT(pPager.jfd) );

			/* Fill in the Pager.zFilename and Pager.zJournal buffers, if required. */
			if (zPathname != null)
			{
				Debug.Assert(nPathname > 0);
				//pPager.zJournal =   (char*)(pPtr += nPathname + 1 + nUri);
				//memcpy(pPager.zFilename, zPathname, nPathname);
				pPager.zFilename = zPathname.ToString();
				zUri = pPager.zFilename;//.Substring( nPathname + 1 );//memcpy( &pPager.zFilename[nPathname + 1], zUri, nUri );
				//memcpy(pPager.zJournal, zPathname, nPathname);
				//memcpy(&pPager.zJournal[nPathname], "-journal", 8);
				pPager.zJournal = pPager.zFilename + "-journal";
				sqlite3FileSuffix3(pPager.zFilename, pPager.zJournal);
#if !SQLITE_OMIT_WAL
pPager.zWal = &pPager.zJournal[nPathname+8+1];
memcpy(pPager.zWal, zPathname, nPathname);
memcpy(&pPager.zWal[nPathname], "-wal", 4);
        sqlite3FileSuffix3(pPager.zFilename, pPager.zWal);
#endif

				//sqlite3_free( ref zPathname );
			}
			else
			{
				pPager.zFilename = "";
			}
			pPager.pVfs = pVfs;
			pPager.vfsFlags = (u32)vfsFlags;

			/* Open the pager file.
			*/
			if (!String.IsNullOrEmpty(zFilename))
			{
				int fout = 0;                    /* VFS flags returned by xOpen() */
				rc = sqlite3OsOpen(pVfs, zFilename, pPager.fd, vfsFlags, ref fout);
				Debug.Assert(0 == memDb);
				readOnly = (fout & SQLITE_OPEN_READONLY) != 0;

				/* If the file was successfully opened for read/write access,
				** choose a default page size in case we have to create the
				** database file. The default page size is the maximum of:
				**
				**    + SQLITE_DEFAULT_PAGE_SIZE,
				**    + The value returned by sqlite3OsSectorSize()
				**    + The largest page size that can be written atomically.
				*/
				if (rc == SQLITE_OK && !readOnly)
				{
					setSectorSize(pPager);
					Debug.Assert(SQLITE_DEFAULT_PAGE_SIZE <= SQLITE_MAX_DEFAULT_PAGE_SIZE);
					if (szPageDflt < pPager.sectorSize)
					{
						if (pPager.sectorSize > SQLITE_MAX_DEFAULT_PAGE_SIZE)
						{
							szPageDflt = SQLITE_MAX_DEFAULT_PAGE_SIZE;
						}
						else
						{
							szPageDflt = (u32)pPager.sectorSize;
						}
					}
#if SQLITE_ENABLE_ATOMIC_WRITE
{
int iDc = sqlite3OsDeviceCharacteristics(pPager.fd);
int ii;
Debug.Assert(SQLITE_IOCAP_ATOMIC512==(512>>8));
Debug.Assert(SQLITE_IOCAP_ATOMIC64K==(65536>>8));
Debug.Assert(SQLITE_MAX_DEFAULT_PAGE_SIZE<=65536);
for(ii=szPageDflt; ii<=SQLITE_MAX_DEFAULT_PAGE_SIZE; ii=ii*2){
if( iDc&(SQLITE_IOCAP_ATOMIC|(ii>>8)) ){
szPageDflt = ii;
}
}
}
#endif
				}
			}
			else
			{
				/* If a temporary file is requested, it is not opened immediately.
				** In this case we accept the default page size and delay actually
				** opening the file until the first call to OsWrite().
				**
				** This branch is also run for an in-memory database. An in-memory
				** database is the same as a temp-file that is never written out to
				** disk and uses an in-memory rollback journal.
				*/
				tempFile = 1;
				pPager.eState = PAGER_READER;
				pPager.eLock = EXCLUSIVE_LOCK;
				readOnly = (vfsFlags & SQLITE_OPEN_READONLY) != 0;
			}

			/* The following call to PagerSetPagesize() serves to set the value of
			** Pager.pageSize and to allocate the Pager.pTmpSpace buffer.
			*/
			if (rc == SQLITE_OK)
			{
				Debug.Assert(pPager.memDb == 0);
				rc = sqlite3PagerSetPagesize(pPager, ref szPageDflt, -1);
				testcase(rc != SQLITE_OK);
			}

			/* If an error occurred in either of the blocks above, free the
			** Pager structure and close the file.
			*/
			if (rc != SQLITE_OK)
			{
				Debug.Assert(null == pPager.pTmpSpace);
				sqlite3OsClose(pPager.fd);
				//sqlite3_free( ref pPager );
				return rc;
			}

			/* Initialize the PCache object. */
			Debug.Assert(nExtra < 1000);
			nExtra = ROUND8(nExtra);
			sqlite3PcacheOpen((int)szPageDflt, nExtra, 0 == memDb,
			0 == memDb ? (dxStress)pagerStress : null, pPager, pPager.pPCache);

			PAGERTRACE("OPEN %d %s\n", FILEHANDLEID(pPager.fd), pPager.zFilename);
			IOTRACE("OPEN %p %s\n", pPager, pPager.zFilename);
			pPager.useJournal = (u8)(useJournal ? 1 : 0);
			pPager.noReadlock = (u8)(noReadlock && readOnly ? 1 : 0);
			/* pPager.stmtOpen = 0; */
			/* pPager.stmtInUse = 0; */
			/* pPager.nRef = 0; */
			/* pPager.stmtSize = 0; */
			/* pPager.stmtJSize = 0; */
			/* pPager.nPage = 0; */
			pPager.mxPgno = SQLITE_MAX_PAGE_COUNT;
			/* pPager.state = PAGER_UNLOCK; */
#if FALSE
Debug.Assert(pPager.state == (tempFile != 0 ? PAGER_EXCLUSIVE : PAGER_UNLOCK));
#endif
			/* pPager.errMask = 0; */
			pPager.tempFile = tempFile != 0;
			Debug.Assert(tempFile == PAGER_LOCKINGMODE_NORMAL
			|| tempFile == PAGER_LOCKINGMODE_EXCLUSIVE);
			Debug.Assert(PAGER_LOCKINGMODE_EXCLUSIVE == 1);
			pPager.exclusiveMode = tempFile != 0;
			pPager.changeCountDone = pPager.tempFile;
			pPager.memDb = memDb;
			pPager.readOnly = readOnly;
			Debug.Assert(useJournal || pPager.tempFile);
			pPager.noSync = pPager.tempFile;
			pPager.fullSync = pPager.noSync;
			pPager.syncFlags = (byte)(pPager.noSync ? 0 : SQLITE_SYNC_NORMAL);
			pPager.ckptSyncFlags = pPager.syncFlags;
			/* pPager.pFirst = 0; */
			/* pPager.pFirstSynced = 0; */
			/* pPager.pLast = 0; */
			pPager.nExtra = (u16)nExtra;
			pPager.journalSizeLimit = SQLITE_DEFAULT_JOURNAL_SIZE_LIMIT;
			Debug.Assert(isOpen(pPager.fd) || tempFile != 0);
			setSectorSize(pPager);
			if (!useJournal)
			{
				pPager.journalMode = PAGER_JOURNALMODE_OFF;
			}
			else if (memDb != 0)
			{
				pPager.journalMode = PAGER_JOURNALMODE_MEMORY;
			}
			/* pPager.xBusyHandler = 0; */
			/* pPager.pBusyHandlerArg = 0; */
			pPager.xReiniter = xReinit;
			/* memset(pPager.aHash, 0, sizeof(pPager.aHash)); */
			ppPager = pPager;
			return SQLITE_OK;
		}

		/*
		** This function is called after transitioning from PAGER_UNLOCK to
		** PAGER_SHARED state. It tests if there is a hot journal present in
		** the file-system for the given pager. A hot journal is one that
		** needs to be played back. According to this function, a hot-journal
		** file exists if the following criteria are met:
		**
		**   * The journal file exists in the file system, and
		**   * No process holds a RESERVED or greater lock on the database file, and
		**   * The database file itself is greater than 0 bytes in size, and
		**   * The first byte of the journal file exists and is not 0x00.
		**
		** If the current size of the database file is 0 but a journal file
		** exists, that is probably an old journal left over from a prior
		** database with the same name. In this case the journal file is
		** just deleted using OsDelete, *pExists is set to 0 and SQLITE_OK
		** is returned.
		**
		** This routine does not check if there is a master journal filename
		** at the end of the file. If there is, and that master journal file
		** does not exist, then the journal file is not really hot. In this
		** case this routine will return a false-positive. The pager_playback()
		** routine will discover that the journal file is not really hot and
		** will not roll it back.
		**
		** If a hot-journal file is found to exist, *pExists is set to 1 and
		** SQLITE_OK returned. If no hot-journal file is present, *pExists is
		** set to 0 and SQLITE_OK returned. If an IO error occurs while trying
		** to determine whether or not a hot-journal file exists, the IO error
		** code is returned and the value of *pExists is undefined.
		*/

		private static int hasHotJournal(Pager pPager, ref int pExists)
		{
			sqlite3_vfs pVfs = pPager.pVfs;
			int rc = SQLITE_OK;           /* Return code */
			int exists = 1;               /* True if a journal file is present */
			int jrnlOpen = isOpen(pPager.jfd) ? 1 : 0;
			Debug.Assert(pPager.useJournal != 0);
			Debug.Assert(isOpen(pPager.fd));
			Debug.Assert(pPager.eState == PAGER_OPEN);

			Debug.Assert(jrnlOpen == 0 || (sqlite3OsDeviceCharacteristics(pPager.jfd) &
			SQLITE_IOCAP_UNDELETABLE_WHEN_OPEN
			) != 0);

			pExists = 0;

			if (0 == jrnlOpen)
			{
				rc = sqlite3OsAccess(pVfs, pPager.zJournal, SQLITE_ACCESS_EXISTS, ref exists);
			}
			if (rc == SQLITE_OK && exists != 0)
			{
				int locked = 0;                 /* True if some process holds a RESERVED lock */

				/* Race condition here:  Another process might have been holding the
				** the RESERVED lock and have a journal open at the sqlite3OsAccess()
				** call above, but then delete the journal and drop the lock before
				** we get to the following sqlite3OsCheckReservedLock() call.  If that
				** is the case, this routine might think there is a hot journal when
				** in fact there is none.  This results in a false-positive which will
				** be dealt with by the playback routine.  Ticket #3883.
				*/
				rc = sqlite3OsCheckReservedLock(pPager.fd, ref locked);
				if (rc == SQLITE_OK && locked == 0)
				{
					Pgno nPage = 0;                 /* Number of pages in database file */

					/* Check the size of the database file. If it consists of 0 pages,
					** then delete the journal file. See the header comment above for
					** the reasoning here.  Delete the obsolete journal file under
					** a RESERVED lock to avoid race conditions and to avoid violating
					** [H33020].
					*/
					rc = pagerPagecount(pPager, ref nPage);
					if (rc == SQLITE_OK)
					{
						if (nPage == 0)
						{
							sqlite3BeginBenignMalloc();
							if (pagerLockDb(pPager, RESERVED_LOCK) == SQLITE_OK)
							{
								sqlite3OsDelete(pVfs, pPager.zJournal, 0);
								if (!pPager.exclusiveMode)
									pagerUnlockDb(pPager, SHARED_LOCK);
							}
							sqlite3EndBenignMalloc();
						}
						else
						{
							/* The journal file exists and no other connection has a reserved
							** or greater lock on the database file. Now check that there is
							** at least one non-zero bytes at the start of the journal file.
							** If there is, then we consider this journal to be hot. If not,
							** it can be ignored.
							*/
							if (0 == jrnlOpen)
							{
								int f = SQLITE_OPEN_READONLY | SQLITE_OPEN_MAIN_JOURNAL;
								rc = sqlite3OsOpen(pVfs, pPager.zJournal, pPager.jfd, f, ref f);
							}
							if (rc == SQLITE_OK)
							{
								u8[] first = new u8[1];
								rc = sqlite3OsRead(pPager.jfd, first, 1, 0);
								if (rc == SQLITE_IOERR_SHORT_READ)
								{
									rc = SQLITE_OK;
								}
								if (0 == jrnlOpen)
								{
									sqlite3OsClose(pPager.jfd);
								}
								pExists = (first[0] != 0) ? 1 : 0;
							}
							else if (rc == SQLITE_CANTOPEN)
							{
								/* If we cannot open the rollback journal file in order to see if
								** its has a zero header, that might be due to an I/O error, or
								** it might be due to the race condition described above and in
								** ticket #3883.  Either way, assume that the journal is hot.
								** This might be a false positive.  But if it is, then the
								** automatic journal playback and recovery mechanism will deal
								** with it under an EXCLUSIVE lock where we do not need to
								** worry so much with race conditions.
								*/
								pExists = 1;
								rc = SQLITE_OK;
							}
						}
					}
				}
			}
			return rc;
		}

		/*
		** This function is called to obtain a shared lock on the database file.
		** It is illegal to call sqlite3PagerAcquire() until after this function
		** has been successfully called. If a shared-lock is already held when
		** this function is called, it is a no-op.
		**
		** The following operations are also performed by this function.
		**
		**   1) If the pager is currently in PAGER_OPEN state (no lock held
		**      on the database file), then an attempt is made to obtain a
		**      SHARED lock on the database file. Immediately after obtaining
		**      the SHARED lock, the file-system is checked for a hot-journal,
		**      which is played back if present. Following any hot-journal
		**      rollback, the contents of the cache are validated by checking
		**      the 'change-counter' field of the database file header and
		**      discarded if they are found to be invalid.
		**
		**   2) If the pager is running in exclusive-mode, and there are currently
		**      no outstanding references to any pages, and is in the error state,
		**      then an attempt is made to clear the error state by discarding
		**      the contents of the page cache and rolling back any open journal
		**      file.
		**
		** If everything is successful, SQLITE_OK is returned. If an IO error
		** occurs while locking the database, checking for a hot-journal file or
		** rolling back a journal file, the IO error code is returned.
		*/

		private static int sqlite3PagerSharedLock(Pager pPager)
		{
			int rc = SQLITE_OK;                /* Return code */

			/* This routine is only called from b-tree and only when there are no
			** outstanding pages. This implies that the pager state should either
			** be OPEN or READER. READER is only possible if the pager is or was in
			** exclusive access mode.
			*/
			Debug.Assert(sqlite3PcacheRefCount(pPager.pPCache) == 0);
			Debug.Assert(assert_pager_state(pPager));
			Debug.Assert(pPager.eState == PAGER_OPEN || pPager.eState == PAGER_READER);
			if (NEVER(
#if SQLITE_OMIT_MEMORYDB
0!=MEMDB
#else
0 != pPager.memDb
#endif
 && pPager.errCode != 0))
			{
				return pPager.errCode;
			}

			if (!pagerUseWal(pPager) && pPager.eState == PAGER_OPEN)
			{
				int bHotJournal = 1;          /* True if there exists a hot journal-file */

				Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
0 == pPager.memDb
#endif
);
				Debug.Assert(pPager.noReadlock == 0 || pPager.readOnly);

				if (pPager.noReadlock == 0)
				{
					rc = pager_wait_on_lock(pPager, SHARED_LOCK);
					if (rc != SQLITE_OK)
					{
						Debug.Assert(pPager.eLock == NO_LOCK || pPager.eLock == UNKNOWN_LOCK);
						goto failed;
					}
				}

				/* If a journal file exists, and there is no RESERVED lock on the
				** database file, then it either needs to be played back or deleted.
				*/
				if (pPager.eLock <= SHARED_LOCK)
				{
					rc = hasHotJournal(pPager, ref bHotJournal);
				}
				if (rc != SQLITE_OK)
				{
					goto failed;
				}
				if (bHotJournal != 0)
				{
					/* Get an EXCLUSIVE lock on the database file. At this point it is
					** important that a RESERVED lock is not obtained on the way to the
					** EXCLUSIVE lock. If it were, another process might open the
					** database file, detect the RESERVED lock, and conclude that the
					** database is safe to read while this process is still rolling the
					** hot-journal back.
					**
					** Because the intermediate RESERVED lock is not requested, any
					** other process attempting to access the database file will get to
					** this point in the code and fail to obtain its own EXCLUSIVE lock
					** on the database file.
					**
					** Unless the pager is in locking_mode=exclusive mode, the lock is
					** downgraded to SHARED_LOCK before this function returns.
					*/
					rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
					if (rc != SQLITE_OK)
					{
						goto failed;
					}

					/* If it is not already open and the file exists on disk, open the
					** journal for read/write access. Write access is required because
					** in exclusive-access mode the file descriptor will be kept open
					** and possibly used for a transaction later on. Also, write-access
					** is usually required to finalize the journal in journal_mode=persist
					** mode (and also for journal_mode=truncate on some systems).
					**
					** If the journal does not exist, it usually means that some
					** other connection managed to get in and roll it back before
					** this connection obtained the exclusive lock above. Or, it
					** may mean that the pager was in the error-state when this
					** function was called and the journal file does not exist.
					*/
					if (!isOpen(pPager.jfd))
					{
						sqlite3_vfs pVfs = pPager.pVfs;
						int bExists = 0;              /* True if journal file exists */
						rc = sqlite3OsAccess(
						pVfs, pPager.zJournal, SQLITE_ACCESS_EXISTS, ref bExists);
						if (rc == SQLITE_OK && bExists != 0)
						{
							int fout = 0;
							int f = SQLITE_OPEN_READWRITE | SQLITE_OPEN_MAIN_JOURNAL;
							Debug.Assert(!pPager.tempFile);
							rc = sqlite3OsOpen(pVfs, pPager.zJournal, pPager.jfd, f, ref fout);
							Debug.Assert(rc != SQLITE_OK || isOpen(pPager.jfd));
							if (rc == SQLITE_OK && (fout & SQLITE_OPEN_READONLY) != 0)
							{
								rc = SQLITE_CANTOPEN_BKPT();
								sqlite3OsClose(pPager.jfd);
							}
						}
					}

					/* Playback and delete the journal.  Drop the database write
					** lock and reacquire the read lock. Purge the cache before
					** playing back the hot-journal so that we don't end up with
					** an inconsistent cache.  Sync the hot journal before playing
					** it back since the process that crashed and left the hot journal
					** probably did not sync it and we are required to always sync
					** the journal before playing it back.
					*/
					if (isOpen(pPager.jfd))
					{
						Debug.Assert(rc == SQLITE_OK);
						rc = pagerSyncHotJournal(pPager);
						if (rc == SQLITE_OK)
						{
							rc = pager_playback(pPager, 1);
							pPager.eState = PAGER_OPEN;
						}
					}
					else if (!pPager.exclusiveMode)
					{
						pagerUnlockDb(pPager, SHARED_LOCK);
					}

					if (rc != SQLITE_OK)
					{
						/* This branch is taken if an error occurs while trying to open
						** or roll back a hot-journal while holding an EXCLUSIVE lock. The
						** pager_unlock() routine will be called before returning to unlock
						** the file. If the unlock attempt fails, then Pager.eLock must be
						** set to UNKNOWN_LOCK (see the comment above the #define for
						** UNKNOWN_LOCK above for an explanation).
						**
						** In order to get pager_unlock() to do this, set Pager.eState to
						** PAGER_ERROR now. This is not actually counted as a transition
						** to ERROR state in the state diagram at the top of this file,
						** since we know that the same call to pager_unlock() will very
						** shortly transition the pager object to the OPEN state. Calling
						** assert_pager_state() would fail now, as it should not be possible
						** to be in ERROR state when there are zero outstanding page
						** references.
						*/
						pager_error(pPager, rc);
						goto failed;
					}

					Debug.Assert(pPager.eState == PAGER_OPEN);
					Debug.Assert((pPager.eLock == SHARED_LOCK)
					|| (pPager.exclusiveMode && pPager.eLock > SHARED_LOCK)
					);
				}

				if (!pPager.tempFile
				&& (pPager.pBackup != null || sqlite3PcachePagecount(pPager.pPCache) > 0)
				)
				{
					/* The shared-lock has just been acquired on the database file
					** and there are already pages in the cache (from a previous
					** read or write transaction).  Check to see if the database
					** has been modified.  If the database has changed, flush the
					** cache.
					**
					** Database changes is detected by looking at 15 bytes beginning
					** at offset 24 into the file.  The first 4 of these 16 bytes are
					** a 32-bit counter that is incremented with each change.  The
					** other bytes change randomly with each file change when
					** a codec is in use.
					**
					** There is a vanishingly small chance that a change will not be
					** detected.  The chance of an undetected change is so small that
					** it can be neglected.
					*/
					Pgno nPage = 0;
					byte[] dbFileVers = new byte[pPager.dbFileVers.Length];

					rc = pagerPagecount(pPager, ref nPage);
					if (rc != 0)
						goto failed;

					if (nPage > 0)
					{
						IOTRACE("CKVERS %p %d\n", pPager, dbFileVers.Length);
						rc = sqlite3OsRead(pPager.fd, dbFileVers, dbFileVers.Length, 24);
						if (rc != SQLITE_OK)
						{
							goto failed;
						}
					}
					else
					{
						Array.Clear(dbFileVers, 0, dbFileVers.Length);// memset( dbFileVers, 0, sizeof( dbFileVers ) );
					}

					if (memcmp(pPager.dbFileVers, dbFileVers, dbFileVers.Length) != 0)
					{
						pager_reset(pPager);
					}
				}

				/* If there is a WAL file in the file-system, open this database in WAL
				** mode. Otherwise, the following function call is a no-op.
				*/
				rc = pagerOpenWalIfPresent(pPager);
#if !SQLITE_OMIT_WAL
Debug.Assert( pPager.pWal == null || rc == SQLITE_OK );
#endif
			}

			if (pagerUseWal(pPager))
			{
				Debug.Assert(rc == SQLITE_OK);
				rc = pagerBeginReadTransaction(pPager);
			}

			if (pPager.eState == PAGER_OPEN && rc == SQLITE_OK)
			{
				rc = pagerPagecount(pPager, ref pPager.dbSize);
			}

		failed:
			if (rc != SQLITE_OK)
			{
				Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
0 == pPager.memDb
#endif
);
				pager_unlock(pPager);
				Debug.Assert(pPager.eState == PAGER_OPEN);
			}
			else
			{
				pPager.eState = PAGER_READER;
			}
			return rc;
		}

		/*
		** If the reference count has reached zero, rollback any active
		** transaction and unlock the pager.
		**
		** Except, in locking_mode=EXCLUSIVE when there is nothing to in
		** the rollback journal, the unlock is not performed and there is
		** nothing to rollback, so this routine is a no-op.
		*/

		private static void pagerUnlockIfUnused(Pager pPager)
		{
			if (sqlite3PcacheRefCount(pPager.pPCache) == 0)
			{
				pagerUnlockAndRollback(pPager);
			}
		}

		/*
		** Acquire a reference to page number pgno in pager pPager (a page
		** reference has type DbPage*). If the requested reference is
		** successfully obtained, it is copied to *ppPage and SQLITE_OK returned.
		**
		** If the requested page is already in the cache, it is returned.
		** Otherwise, a new page object is allocated and populated with data
		** read from the database file. In some cases, the pcache module may
		** choose not to allocate a new page object and may reuse an existing
		** object with no outstanding references.
		**
		** The extra data appended to a page is always initialized to zeros the
		** first time a page is loaded into memory. If the page requested is
		** already in the cache when this function is called, then the extra
		** data is left as it was when the page object was last used.
		**
		** If the database image is smaller than the requested page or if a
		** non-zero value is passed as the noContent parameter and the
		** requested page is not already stored in the cache, then no
		** actual disk read occurs. In this case the memory image of the
		** page is initialized to all zeros.
		**
		** If noContent is true, it means that we do not care about the contents
		** of the page. This occurs in two seperate scenarios:
		**
		**   a) When reading a free-list leaf page from the database, and
		**
		**   b) When a savepoint is being rolled back and we need to load
		**      a new page into the cache to be filled with the data read
		**      from the savepoint journal.
		**
		** If noContent is true, then the data returned is zeroed instead of
		** being read from the database. Additionally, the bits corresponding
		** to pgno in Pager.pInJournal (bitvec of pages already written to the
		** journal file) and the PagerSavepoint.pInSavepoint bitvecs of any open
		** savepoints are set. This means if the page is made writable at any
		** point in the future, using a call to sqlite3PagerWrite(), its contents
		** will not be journaled. This saves IO.
		**
		** The acquisition might fail for several reasons.  In all cases,
		** an appropriate error code is returned and *ppPage is set to NULL.
		**
		** See also sqlite3PagerLookup().  Both this routine and Lookup() attempt
		** to find a page in the in-memory cache first.  If the page is not already
		** in memory, this routine goes to disk to read it in whereas Lookup()
		** just returns 0.  This routine acquires a read-lock the first time it
		** has to go to disk, and could also playback an old journal if necessary.
		** Since Lookup() never goes to disk, it never has to deal with locks
		** or journal files.
		*/

		// Under C# from the header file
		//#define sqlite3PagerGet(A,B,C) sqlite3PagerAcquire(A,B,C,0)

		private static int sqlite3PagerGet(
		Pager pPager,       /* The pager open on the database file */
		u32 pgno,          /* Page number to fetch */
		ref DbPage ppPage   /* Write a pointer to the page here */
		)
		{
			return sqlite3PagerAcquire(pPager, pgno, ref ppPage, 0);
		}

		private static int sqlite3PagerAcquire(
		Pager pPager,      /* The pager open on the database file */
		u32 pgno,          /* Page number to fetch */
		ref DbPage ppPage, /* Write a pointer to the page here */
		u8 noContent     /* Do not bother reading content from disk if true */
		)
		{
			int rc;
			PgHdr pPg = null;

			Debug.Assert(pPager.eState >= PAGER_READER);
			Debug.Assert(assert_pager_state(pPager));
			if (pgno == 0)
			{
				return SQLITE_CORRUPT_BKPT();
			}

			/* If the pager is in the error state, return an error immediately.
			** Otherwise, request the page from the PCache layer. */
			if (pPager.errCode != SQLITE_OK)
			{
				rc = pPager.errCode;
			}
			else
			{
				rc = sqlite3PcacheFetch(pPager.pPCache, pgno, 1, ref ppPage);
			}

			if (rc != SQLITE_OK)
			{
				/* Either the call to sqlite3PcacheFetch() returned an error or the
				** pager was already in the error-state when this function was called.
				** Set pPg to 0 and jump to the exception handler.  */
				pPg = null;
				goto pager_acquire_err;
			}
			Debug.Assert((ppPage).pgno == pgno);
			Debug.Assert((ppPage).pPager == pPager || (ppPage).pPager == null);

			if ((ppPage).pPager != null && 0 == noContent)
			{
				/* In this case the pcache already contains an initialized copy of
				** the page. Return without further ado.  */
				Debug.Assert(pgno <= PAGER_MAX_PGNO && pgno != PAGER_MJ_PGNO(pPager));
				PAGER_INCR(ref pPager.nHit);
				return SQLITE_OK;
			}
			else
			{
				/* The pager cache has created a new page. Its content needs to
				** be initialized.  */
#if SQLITE_TEST
        PAGER_INCR( ref pPager.nMiss );
#endif
				pPg = ppPage;
				pPg.pPager = pPager;
				pPg.pExtra = new MemPage();//memset(pPg.pExtra, 0, pPager.nExtra);

				/* The maximum page number is 2^31. Return SQLITE_CORRUPT if a page
				** number greater than this, or the unused locking-page, is requested. */
				if (pgno > PAGER_MAX_PGNO || pgno == PAGER_MJ_PGNO(pPager))
				{
					rc = SQLITE_CORRUPT_BKPT();
					goto pager_acquire_err;
				}
				if (
#if SQLITE_OMIT_MEMORYDB
1==MEMDB
#else
pPager.memDb != 0
#endif
 || pPager.dbSize < pgno || noContent != 0 || !isOpen(pPager.fd))
				{
					if (pgno > pPager.mxPgno)
					{
						rc = SQLITE_FULL;
						goto pager_acquire_err;
					}
					if (noContent != 0)
					{
						/* Failure to set the bits in the InJournal bit-vectors is benign.
						** It merely means that we might do some extra work to journal a
						** page that does not need to be journaled.  Nevertheless, be sure
						** to test the case where a malloc error occurs while trying to set
						** a bit in a bit vector.
						*/
						sqlite3BeginBenignMalloc();
						if (pgno <= pPager.dbOrigSize)
						{
#if !NDEBUG || SQLITE_COVERAGE_TEST
							rc = sqlite3BitvecSet(pPager.pInJournal, pgno);          //TESTONLY( rc = ) sqlite3BitvecSet(pPager.pInJournal, pgno);
#else
sqlite3BitvecSet(pPager.pInJournal, pgno);
#endif
							testcase(rc == SQLITE_NOMEM);
						}
#if !NDEBUG || SQLITE_COVERAGE_TEST
						rc = addToSavepointBitvecs(pPager, pgno); //TESTONLY( rc = ) addToSavepointBitvecs(pPager, pgno);
#else
addToSavepointBitvecs(pPager, pgno);
#endif

						testcase(rc == SQLITE_NOMEM);
						sqlite3EndBenignMalloc();
					}
					//memset(pPg.pData, 0, pPager.pageSize);
					Array.Clear(pPg.pData, 0, pPager.pageSize);
					IOTRACE("ZERO %p %d\n", pPager, pgno);
				}
				else
				{
					Debug.Assert(pPg.pPager == pPager);
					rc = readDbPage(pPg);
					if (rc != SQLITE_OK)
					{
						goto pager_acquire_err;
					}
				}

				pager_set_pagehash(pPg);
			}
			return SQLITE_OK;

		pager_acquire_err:
			Debug.Assert(rc != SQLITE_OK);
			if (pPg != null)
			{
				sqlite3PcacheDrop(pPg);
			}
			pagerUnlockIfUnused(pPager);

			ppPage = null;
			return rc;
		}

		/*
		** Acquire a page if it is already in the in-memory cache.  Do
		** not read the page from disk.  Return a pointer to the page,
		** or 0 if the page is not in cache.
		**
		** See also sqlite3PagerGet().  The difference between this routine
		** and sqlite3PagerGet() is that _get() will go to the disk and read
		** in the page if the page is not already in cache.  This routine
		** returns NULL if the page is not in cache or if a disk I/O error
		** has ever happened.
		*/

		private static DbPage sqlite3PagerLookup(Pager pPager, u32 pgno)
		{
			PgHdr pPg = null;

			Debug.Assert(pPager != null);
			Debug.Assert(pgno != 0);
			Debug.Assert(pPager.pPCache != null);
			Debug.Assert(pPager.eState >= PAGER_READER && pPager.eState != PAGER_ERROR);
			sqlite3PcacheFetch(pPager.pPCache, pgno, 0, ref pPg);

			return pPg;
		}

		/*
		** Release a page reference.
		**
		** If the number of references to the page drop to zero, then the
		** page is added to the LRU list.  When all references to all pages
		** are released, a rollback occurs and the lock on the database is
		** removed.
		*/

		private static void sqlite3PagerUnref(DbPage pPg)
		{
			if (pPg != null)
			{
				Pager pPager = pPg.pPager;
				sqlite3PcacheRelease(pPg);
				pagerUnlockIfUnused(pPager);
			}
		}

		/*
		** This function is called at the start of every write transaction.
		** There must already be a RESERVED or EXCLUSIVE lock on the database
		** file when this routine is called.
		**
		** Open the journal file for pager pPager and write a journal header
		** to the start of it. If there are active savepoints, open the sub-journal
		** as well. This function is only used when the journal file is being
		** opened to write a rollback log for a transaction. It is not used
		** when opening a hot journal file to roll it back.
		**
		** If the journal file is already open (as it may be in exclusive mode),
		** then this function just writes a journal header to the start of the
		** already open file.
		**
		** Whether or not the journal file is opened by this function, the
		** Pager.pInJournal bitvec structure is allocated.
		**
		** Return SQLITE_OK if everything is successful. Otherwise, return
		** SQLITE_NOMEM if the attempt to allocate Pager.pInJournal fails, or
		** an IO error code if opening or writing the journal file fails.
		*/

		private static int pager_open_journal(Pager pPager)
		{
			int rc = SQLITE_OK;                        /* Return code */
			sqlite3_vfs pVfs = pPager.pVfs;            /* Local cache of vfs pointer */

			Debug.Assert(pPager.eState == PAGER_WRITER_LOCKED);
			Debug.Assert(assert_pager_state(pPager));
			Debug.Assert(pPager.pInJournal == null);

			/* If already in the error state, this function is a no-op.  But on
			** the other hand, this routine is never called if we are already in
			** an error state. */
			if (NEVER(pPager.errCode) != 0)
				return pPager.errCode;

			if (!pagerUseWal(pPager) && pPager.journalMode != PAGER_JOURNALMODE_OFF)
			{
				pPager.pInJournal = sqlite3BitvecCreate(pPager.dbSize);
				//if (pPager.pInJournal == null)
				//{
				//  return SQLITE_NOMEM;
				//}

				/* Open the journal file if it is not already open. */
				if (!isOpen(pPager.jfd))
				{
					if (pPager.journalMode == PAGER_JOURNALMODE_MEMORY)
					{
						sqlite3MemJournalOpen(pPager.jfd);
					}
					else
					{
						int flags =                   /* VFS flags to open journal file */
						SQLITE_OPEN_READWRITE | SQLITE_OPEN_CREATE |
						(pPager.tempFile ?
						(SQLITE_OPEN_DELETEONCLOSE | SQLITE_OPEN_TEMP_JOURNAL) :
						(SQLITE_OPEN_MAIN_JOURNAL)
						);
#if SQLITE_ENABLE_ATOMIC_WRITE
rc = sqlite3JournalOpen(
pVfs, pPager.zJournal, pPager.jfd, flags, jrnlBufferSize(pPager)
);
#else
						int int0 = 0;
						rc = sqlite3OsOpen(pVfs, pPager.zJournal, pPager.jfd, flags, ref int0);
#endif
					}
					Debug.Assert(rc != SQLITE_OK || isOpen(pPager.jfd));
				}

				/* Write the first journal header to the journal file and open
				** the sub-journal if necessary.
				*/
				if (rc == SQLITE_OK)
				{
					/* TODO: Check if all of these are really required. */
					pPager.nRec = 0;
					pPager.journalOff = 0;
					pPager.setMaster = 0;
					pPager.journalHdr = 0;
					rc = writeJournalHdr(pPager);
				}
			}
			if (rc != SQLITE_OK)
			{
				sqlite3BitvecDestroy(ref pPager.pInJournal);
				pPager.pInJournal = null;
			}
			else
			{
				Debug.Assert(pPager.eState == PAGER_WRITER_LOCKED);
				pPager.eState = PAGER_WRITER_CACHEMOD;
			}
			return rc;
		}

		/*
		** Begin a write-transaction on the specified pager object. If a
		** write-transaction has already been opened, this function is a no-op.
		**
		** If the exFlag argument is false, then acquire at least a RESERVED
		** lock on the database file. If exFlag is true, then acquire at least
		** an EXCLUSIVE lock. If such a lock is already held, no locking
		** functions need be called.
		**
		** If the subjInMemory argument is non-zero, then any sub-journal opened
		** within this transaction will be opened as an in-memory file. This
		** has no effect if the sub-journal is already opened (as it may be when
		** running in exclusive mode) or if the transaction does not require a
		** sub-journal. If the subjInMemory argument is zero, then any required
		** sub-journal is implemented in-memory if pPager is an in-memory database,
		** or using a temporary file otherwise.
		*/

		private static int sqlite3PagerBegin(Pager pPager, bool exFlag, int subjInMemory)
		{
			int rc = SQLITE_OK;
			if (pPager.errCode != 0)
				return pPager.errCode;
			Debug.Assert(pPager.eState >= PAGER_READER && pPager.eState < PAGER_ERROR);
			pPager.subjInMemory = (u8)subjInMemory;
			if (ALWAYS(pPager.eState == PAGER_READER))
			{
				Debug.Assert(pPager.pInJournal == null);
				if (pagerUseWal(pPager))
				{
					/* If the pager is configured to use locking_mode=exclusive, and an
					** exclusive lock on the database is not already held, obtain it now.
					*/
					if (pPager.exclusiveMode && sqlite3WalExclusiveMode(pPager.pWal, -1))
					{
						rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
						if (rc != SQLITE_OK)
						{
							return rc;
						}
						sqlite3WalExclusiveMode(pPager.pWal, 1);
					}

					/* Grab the write lock on the log file. If successful, upgrade to
					** PAGER_RESERVED state. Otherwise, return an error code to the caller.
					** The busy-handler is not invoked if another connection already
					** holds the write-lock. If possible, the upper layer will call it.
					*/
					rc = sqlite3WalBeginWriteTransaction(pPager.pWal);
				}
				else
				{
					/* Obtain a RESERVED lock on the database file. If the exFlag parameter
					** is true, then immediately upgrade this to an EXCLUSIVE lock. The
					** busy-handler callback can be used when upgrading to the EXCLUSIVE
					** lock, but not when obtaining the RESERVED lock.
					*/
					rc = pagerLockDb(pPager, RESERVED_LOCK);
					if (rc == SQLITE_OK && exFlag)
					{
						rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
					}
				}

				if (rc == SQLITE_OK)
				{
					/* Change to WRITER_LOCKED state.
					**
					** WAL mode sets Pager.eState to PAGER_WRITER_LOCKED or CACHEMOD
					** when it has an open transaction, but never to DBMOD or FINISHED.
					** This is because in those states the code to roll back savepoint
					** transactions may copy data from the sub-journal into the database
					** file as well as into the page cache. Which would be incorrect in
					** WAL mode.
					*/
					pPager.eState = PAGER_WRITER_LOCKED;
					pPager.dbHintSize = pPager.dbSize;
					pPager.dbFileSize = pPager.dbSize;
					pPager.dbOrigSize = pPager.dbSize;
					pPager.journalOff = 0;
				}

				Debug.Assert(rc == SQLITE_OK || pPager.eState == PAGER_READER);
				Debug.Assert(rc != SQLITE_OK || pPager.eState == PAGER_WRITER_LOCKED);
				Debug.Assert(assert_pager_state(pPager));
			}

			PAGERTRACE("TRANSACTION %d\n", PAGERID(pPager));
			return rc;
		}

		/*
		** Mark a single data page as writeable. The page is written into the
		** main journal or sub-journal as required. If the page is written into
		** one of the journals, the corresponding bit is set in the
		** Pager.pInJournal bitvec and the PagerSavepoint.pInSavepoint bitvecs
		** of any open savepoints as appropriate.
		*/

		private static int pager_write(PgHdr pPg)
		{
			byte[] pData = pPg.pData;
			Pager pPager = pPg.pPager;
			int rc = SQLITE_OK;

			/* This routine is not called unless a write-transaction has already
			** been started. The journal file may or may not be open at this point.
			** It is never called in the ERROR state.
			*/
			Debug.Assert(pPager.eState == PAGER_WRITER_LOCKED
			|| pPager.eState == PAGER_WRITER_CACHEMOD
			|| pPager.eState == PAGER_WRITER_DBMOD
			);
			Debug.Assert(assert_pager_state(pPager));

			/* If an error has been previously detected, report the same error
			** again. This should not happen, but the check provides robustness. */
			if (NEVER(pPager.errCode) != 0)
				return pPager.errCode;

			/* Higher-level routines never call this function if database is not
			** writable.  But check anyway, just for robustness. */
			if (NEVER(pPager.readOnly))
				return SQLITE_PERM;

#if SQLITE_CHECK_PAGES
CHECK_PAGE(pPg);
#endif
			/* The journal file needs to be opened. Higher level routines have already
** obtained the necessary locks to begin the write-transaction, but the
** rollback journal might not yet be open. Open it now if this is the case.
**
** This is done before calling sqlite3PcacheMakeDirty() on the page.
** Otherwise, if it were done after calling sqlite3PcacheMakeDirty(), then
** an error might occur and the pager would end up in WRITER_LOCKED state
** with pages marked as dirty in the cache.
*/
			if (pPager.eState == PAGER_WRITER_LOCKED)
			{
				rc = pager_open_journal(pPager);
				if (rc != SQLITE_OK)
					return rc;
			}
			Debug.Assert(pPager.eState >= PAGER_WRITER_CACHEMOD);
			Debug.Assert(assert_pager_state(pPager));

			/* Mark the page as dirty.  If the page has already been written
			** to the journal then we can return right away.
			*/
			sqlite3PcacheMakeDirty(pPg);
			if (pageInJournal(pPg) && !subjRequiresPage(pPg))
			{
				Debug.Assert(!pagerUseWal(pPager));
			}
			else
			{
				/* The transaction journal now exists and we have a RESERVED or an
				** EXCLUSIVE lock on the main database file.  Write the current page to
				** the transaction journal if it is not there already.
				*/
				if (!pageInJournal(pPg) && !pagerUseWal(pPager))
				{
					Debug.Assert(pagerUseWal(pPager) == false);
					if (pPg.pgno <= pPager.dbOrigSize && isOpen(pPager.jfd))
					{
						u32 cksum;
						byte[] pData2 = null;
						i64 iOff = pPager.journalOff;

						/* We should never write to the journal file the page that
						** contains the database locks.  The following Debug.Assert verifies
						** that we do not. */
						Debug.Assert(pPg.pgno != ((PENDING_BYTE / (pPager.pageSize)) + 1));//PAGER_MJ_PGNO(pPager) );

						Debug.Assert(pPager.journalHdr <= pPager.journalOff);
						if (CODEC2(pPager, pData, pPg.pgno, SQLITE_ENCRYPT_READ_CTX, ref pData2))
							return SQLITE_NOMEM;  // CODEC2(pPager, pData, pPg.pgno, 7, return SQLITE_NOMEM, pData2);
						cksum = pager_cksum(pPager, pData2);

						/* Even if an IO or diskfull error occurred while journalling the
						** page in the block above, set the need-sync flag for the page.
						** Otherwise, when the transaction is rolled back, the logic in
						** playback_one_page() will think that the page needs to be restored
						** in the database file. And if an IO error occurs while doing so,
						** then corruption may follow.
						*/

						pPg.flags |= PGHDR_NEED_SYNC;

						rc = write32bits(pPager.jfd, iOff, pPg.pgno);
						if (rc != SQLITE_OK)
							return rc;
						rc = sqlite3OsWrite(pPager.jfd, pData2, pPager.pageSize, iOff + 4);
						if (rc != SQLITE_OK)
							return rc;
						rc = write32bits(pPager.jfd, iOff + pPager.pageSize + 4, cksum);
						if (rc != SQLITE_OK)
							return rc;

						IOTRACE("JOUT %p %d %lld %d\n", pPager, pPg.pgno,
						pPager.journalOff, pPager.pageSize);
#if SQLITE_TEST
#if !TCLSH
            PAGER_INCR( ref sqlite3_pager_writej_count );
#else
            int iValue = sqlite3_pager_writej_count.iValue;
            PAGER_INCR( ref iValue );
            sqlite3_pager_writej_count.iValue = iValue;
#endif
#endif
						PAGERTRACE("JOURNAL %d page %d needSync=%d hash(%08x)\n",
						PAGERID(pPager), pPg.pgno,
						((pPg.flags & PGHDR_NEED_SYNC) != 0 ? 1 : 0), pager_pagehash(pPg));

						pPager.journalOff += 8 + pPager.pageSize;
						pPager.nRec++;
						Debug.Assert(pPager.pInJournal != null);
						rc = sqlite3BitvecSet(pPager.pInJournal, pPg.pgno);
						testcase(rc == SQLITE_NOMEM);
						Debug.Assert(rc == SQLITE_OK || rc == SQLITE_NOMEM);
						rc |= addToSavepointBitvecs(pPager, pPg.pgno);
						if (rc != SQLITE_OK)
						{
							Debug.Assert(rc == SQLITE_NOMEM);
							return rc;
						}
					}
					else
					{
						if (pPager.eState != PAGER_WRITER_DBMOD)
						{
							pPg.flags |= PGHDR_NEED_SYNC;
						}
						PAGERTRACE("APPEND %d page %d needSync=%d\n",
						PAGERID(pPager), pPg.pgno,
						((pPg.flags & PGHDR_NEED_SYNC) != 0 ? 1 : 0));
					}
				}

				/* If the statement journal is open and the page is not in it,
				** then write the current page to the statement journal.  Note that
				** the statement journal format differs from the standard journal format
				** in that it omits the checksums and the header.
				*/
				if (subjRequiresPage(pPg))
				{
					rc = subjournalPage(pPg);
				}
			}

			/* Update the database size and return.
			*/
			if (pPager.dbSize < pPg.pgno)
			{
				pPager.dbSize = pPg.pgno;
			}
			return rc;
		}

		/*
		** Mark a data page as writeable. This routine must be called before
		** making changes to a page. The caller must check the return value
		** of this function and be careful not to change any page data unless
		** this routine returns SQLITE_OK.
		**
		** The difference between this function and pager_write() is that this
		** function also deals with the special case where 2 or more pages
		** fit on a single disk sector. In this case all co-resident pages
		** must have been written to the journal file before returning.
		**
		** If an error occurs, SQLITE_NOMEM or an IO error code is returned
		** as appropriate. Otherwise, SQLITE_OK.
		*/

		private static int sqlite3PagerWrite(DbPage pDbPage)
		{
			int rc = SQLITE_OK;

			PgHdr pPg = pDbPage;
			Pager pPager = pPg.pPager;
			u32 nPagePerSector = (u32)(pPager.sectorSize / pPager.pageSize);

			Debug.Assert(pPager.eState >= PAGER_WRITER_LOCKED);
			Debug.Assert(pPager.eState != PAGER_ERROR);
			Debug.Assert(assert_pager_state(pPager));

			if (nPagePerSector > 1)
			{
				Pgno nPageCount = 0;     /* Total number of pages in database file */
				Pgno pg1;                /* First page of the sector pPg is located on. */
				Pgno nPage = 0;          /* Number of pages starting at pg1 to journal */
				int ii;                  /* Loop counter */
				bool needSync = false;   /* True if any page has PGHDR_NEED_SYNC */

				/* Set the doNotSyncSpill flag to 1. This is because we cannot allow
				** a journal header to be written between the pages journaled by
				** this function.
				*/
				Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
0 == pPager.memDb
#endif
);
				Debug.Assert(pPager.doNotSyncSpill == 0);
				pPager.doNotSyncSpill++;

				/* This trick assumes that both the page-size and sector-size are
				** an integer power of 2. It sets variable pg1 to the identifier
				** of the first page of the sector pPg is located on.
				*/
				pg1 = (u32)((pPg.pgno - 1) & ~(nPagePerSector - 1)) + 1;

				nPageCount = pPager.dbSize;
				if (pPg.pgno > nPageCount)
				{
					nPage = (pPg.pgno - pg1) + 1;
				}
				else if ((pg1 + nPagePerSector - 1) > nPageCount)
				{
					nPage = nPageCount + 1 - pg1;
				}
				else
				{
					nPage = nPagePerSector;
				}
				Debug.Assert(nPage > 0);
				Debug.Assert(pg1 <= pPg.pgno);
				Debug.Assert((pg1 + nPage) > pPg.pgno);

				for (ii = 0; ii < nPage && rc == SQLITE_OK; ii++)
				{
					u32 pg = (u32)(pg1 + ii);
					PgHdr pPage = new PgHdr();
					if (pg == pPg.pgno || sqlite3BitvecTest(pPager.pInJournal, pg) == 0)
					{
						if (pg != ((PENDING_BYTE / (pPager.pageSize)) + 1)) //PAGER_MJ_PGNO(pPager))
						{
							rc = sqlite3PagerGet(pPager, pg, ref pPage);
							if (rc == SQLITE_OK)
							{
								rc = pager_write(pPage);
								if ((pPage.flags & PGHDR_NEED_SYNC) != 0)
								{
									needSync = true;
								}
								sqlite3PagerUnref(pPage);
							}
						}
					}
					else if ((pPage = pager_lookup(pPager, pg)) != null)
					{
						if ((pPage.flags & PGHDR_NEED_SYNC) != 0)
						{
							needSync = true;
						}
						sqlite3PagerUnref(pPage);
					}
				}

				/* If the PGHDR_NEED_SYNC flag is set for any of the nPage pages
				** starting at pg1, then it needs to be set for all of them. Because
				** writing to any of these nPage pages may damage the others, the
				** journal file must contain sync()ed copies of all of them
				** before any of them can be written out to the database file.
				*/
				if (rc == SQLITE_OK && needSync)
				{
					Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
0 == pPager.memDb
#endif
);
					for (ii = 0; ii < nPage; ii++)
					{
						PgHdr pPage = pager_lookup(pPager, (u32)(pg1 + ii));
						if (pPage != null)
						{
							pPage.flags |= PGHDR_NEED_SYNC;
							sqlite3PagerUnref(pPage);
						}
					}
				}

				Debug.Assert(pPager.doNotSyncSpill == 1);
				pPager.doNotSyncSpill--;
			}
			else
			{
				rc = pager_write(pDbPage);
			}
			return rc;
		}

		/*
		** Return TRUE if the page given in the argument was previously passed
		** to sqlite3PagerWrite().  In other words, return TRUE if it is ok
		** to change the content of the page.
		*/
#if !NDEBUG

		private static bool sqlite3PagerIswriteable(DbPage pPg)
		{
			return (pPg.flags & PGHDR_DIRTY) != 0;
		}

#else
static bool sqlite3PagerIswriteable( DbPage pPg ) { return true; }
#endif

		/*
** A call to this routine tells the pager that it is not necessary to
** write the information on page pPg back to the disk, even though
** that page might be marked as dirty.  This happens, for example, when
** the page has been added as a leaf of the freelist and so its
** content no longer matters.
**
** The overlying software layer calls this routine when all of the data
** on the given page is unused. The pager marks the page as clean so
** that it does not get written to disk.
**
** Tests show that this optimization can quadruple the speed of large
** DELETE operations.
*/

		private static void sqlite3PagerDontWrite(PgHdr pPg)
		{
			Pager pPager = pPg.pPager;

			if ((pPg.flags & PGHDR_DIRTY) != 0 && pPager.nSavepoint == 0)
			{
				PAGERTRACE("DONT_WRITE page %d of %d\n", pPg.pgno, PAGERID(pPager));
				IOTRACE("CLEAN %p %d\n", pPager, pPg.pgno);
				pPg.flags |= PGHDR_DONT_WRITE;
				pager_set_pagehash(pPg);
			}
		}

		/*
		** This routine is called to increment the value of the database file
		** change-counter, stored as a 4-byte big-endian integer starting at
		** byte offset 24 of the pager file.  The secondary change counter at
		** 92 is also updated, as is the SQLite version number at offset 96.
		**
		** But this only happens if the pPager.changeCountDone flag is false.
		** To avoid excess churning of page 1, the update only happens once.
		** See also the pager_write_changecounter() routine that does an
		** unconditional update of the change counters.
		**
		** If the isDirectMode flag is zero, then this is done by calling
		** sqlite3PagerWrite() on page 1, then modifying the contents of the
		** page data. In this case the file will be updated when the current
		** transaction is committed.
		**
		** The isDirectMode flag may only be non-zero if the library was compiled
		** with the SQLITE_ENABLE_ATOMIC_WRITE macro defined. In this case,
		** if isDirect is non-zero, then the database file is updated directly
		** by writing an updated version of page 1 using a call to the
		** sqlite3OsWrite() function.
		*/

		private static int pager_incr_changecounter(Pager pPager, bool isDirectMode)
		{
			int rc = SQLITE_OK;

			Debug.Assert(pPager.eState == PAGER_WRITER_CACHEMOD
			|| pPager.eState == PAGER_WRITER_DBMOD
			);
			Debug.Assert(assert_pager_state(pPager));

			/* Declare and initialize constant integer 'isDirect'. If the
			** atomic-write optimization is enabled in this build, then isDirect
			** is initialized to the value passed as the isDirectMode parameter
			** to this function. Otherwise, it is always set to zero.
			**
			** The idea is that if the atomic-write optimization is not
			** enabled at compile time, the compiler can omit the tests of
			** 'isDirect' below, as well as the block enclosed in the
			** "if( isDirect )" condition.
			*/
#if !SQLITE_ENABLE_ATOMIC_WRITE
			//# define DIRECT_MODE 0
			bool DIRECT_MODE = false;
			Debug.Assert(isDirectMode == false);
			UNUSED_PARAMETER(isDirectMode);
#else
//# define DIRECT_MODE isDirectMode
int DIRECT_MODE = isDirectMode;
#endif

			if (!pPager.changeCountDone && pPager.dbSize > 0)
			{
				PgHdr pPgHdr = null;            /* Reference to page 1 */

				Debug.Assert(!pPager.tempFile && isOpen(pPager.fd));

				/* Open page 1 of the file for writing. */
				rc = sqlite3PagerGet(pPager, 1, ref pPgHdr);
				Debug.Assert(pPgHdr == null || rc == SQLITE_OK);

				/* If page one was fetched successfully, and this function is not
				** operating in direct-mode, make page 1 writable.  When not in
				** direct mode, page 1 is always held in cache and hence the PagerGet()
				** above is always successful - hence the ALWAYS on rc==SQLITE_OK.
				*/
				if (!DIRECT_MODE && ALWAYS(rc == SQLITE_OK))
				{
					rc = sqlite3PagerWrite(pPgHdr);
				}

				if (rc == SQLITE_OK)
				{
					/* Actually do the update of the change counter */
					pager_write_changecounter(pPgHdr);

					/* If running in direct mode, write the contents of page 1 to the file. */
					if (DIRECT_MODE)
					{
						u8[] zBuf = null;
						Debug.Assert(pPager.dbFileSize > 0);
						if (CODEC2(pPager, pPgHdr.pData, 1, SQLITE_ENCRYPT_WRITE_CTX, ref zBuf))
							return rc = SQLITE_NOMEM;//CODEC2(pPager, pPgHdr.pData, 1, 6, rc=SQLITE_NOMEM, zBuf);
						if (rc == SQLITE_OK)
						{
							rc = sqlite3OsWrite(pPager.fd, zBuf, pPager.pageSize, 0);
						}

						if (rc == SQLITE_OK)
						{
							pPager.changeCountDone = true;
						}
					}
					else
					{
						pPager.changeCountDone = true;
					}
				}

				/* Release the page reference. */
				sqlite3PagerUnref(pPgHdr);
			}
			return rc;
		}

		/*
		** Sync the database file to disk. This is a no-op for in-memory databases
		** or pages with the Pager.noSync flag set.
		**
		** If successful, or if called on a pager for which it is a no-op, this
		** function returns SQLITE_OK. Otherwise, an IO error code is returned.
		*/

		private static int sqlite3PagerSync(Pager pPager)
		{
			long rc = SQLITE_OK;
			if (!pPager.noSync)
			{
				Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0 == MEMDB
#else
0 == pPager.memDb
#endif
);
				rc = sqlite3OsSync(pPager.fd, pPager.syncFlags);
			}
			else if (isOpen(pPager.fd))
			{
				Debug.Assert(
#if SQLITE_OMIT_MEMORYDB
0 == MEMDB
#else
0 == pPager.memDb
#endif
);
				sqlite3OsFileControl(pPager.fd, SQLITE_FCNTL_SYNC_OMITTED, ref rc);
			}
			return (int)rc;
		}

		/*
		** This function may only be called while a write-transaction is active in
		** rollback. If the connection is in WAL mode, this call is a no-op.
		** Otherwise, if the connection does not already have an EXCLUSIVE lock on
		** the database file, an attempt is made to obtain one.
		**
		** If the EXCLUSIVE lock is already held or the attempt to obtain it is
		** successful, or the connection is in WAL mode, SQLITE_OK is returned.
		** Otherwise, either SQLITE_BUSY or an SQLITE_IOERR_XXX error code is
		** returned.
		*/

		private static int sqlite3PagerExclusiveLock(Pager pPager)
		{
			int rc = SQLITE_OK;
			Debug.Assert(pPager.eState == PAGER_WRITER_CACHEMOD
			|| pPager.eState == PAGER_WRITER_DBMOD
			|| pPager.eState == PAGER_WRITER_LOCKED
			);
			Debug.Assert(assert_pager_state(pPager));
			if (false == pagerUseWal(pPager))
			{
				rc = pager_wait_on_lock(pPager, EXCLUSIVE_LOCK);
			}
			return rc;
		}

		/*
		** Sync the database file for the pager pPager. zMaster points to the name
		** of a master journal file that should be written into the individual
		** journal file. zMaster may be NULL, which is interpreted as no master
		** journal (a single database transaction).
		**
		** This routine ensures that:
		**
		**   * The database file change-counter is updated,
		**   * the journal is synced (unless the atomic-write optimization is used),
		**   * all dirty pages are written to the database file,
		**   * the database file is truncated (if required), and
		**   * the database file synced.
		**
		** The only thing that remains to commit the transaction is to finalize
		** (delete, truncate or zero the first part of) the journal file (or
		** delete the master journal file if specified).
		**
		** Note that if zMaster==NULL, this does not overwrite a previous value
		** passed to an sqlite3PagerCommitPhaseOne() call.
		**
		** If the final parameter - noSync - is true, then the database file itself
		** is not synced. The caller must call sqlite3PagerSync() directly to
		** sync the database file before calling CommitPhaseTwo() to delete the
		** journal file in this case.
		*/

		private static int sqlite3PagerCommitPhaseOne(
		Pager pPager,         /* Pager object */
		string zMaster,       /* If not NULL, the master journal name */
		bool noSync           /* True to omit the xSync on the db file */
		)
		{
			int rc = SQLITE_OK;             /* Return code */

			Debug.Assert(pPager.eState == PAGER_WRITER_LOCKED
			|| pPager.eState == PAGER_WRITER_CACHEMOD
			|| pPager.eState == PAGER_WRITER_DBMOD
			|| pPager.eState == PAGER_ERROR
			);
			Debug.Assert(assert_pager_state(pPager));

			/* If a prior error occurred, report that error again. */
			if (NEVER(pPager.errCode != 0))
				return pPager.errCode;

			PAGERTRACE("DATABASE SYNC: File=%s zMaster=%s nSize=%d\n",
			pPager.zFilename, zMaster, pPager.dbSize);

			/* If no database changes have been made, return early. */
			if (pPager.eState < PAGER_WRITER_CACHEMOD)
				return SQLITE_OK;

			if (
#if SQLITE_OMIT_MEMORYDB
0 != MEMDB
#else
0 != pPager.memDb
#endif
)
			{
				/* If this is an in-memory db, or no pages have been written to, or this
				** function has already been called, it is mostly a no-op.  However, any
				** backup in progress needs to be restarted.
				*/
				sqlite3BackupRestart(pPager.pBackup);
			}
			else
			{
				if (pagerUseWal(pPager))
				{
					PgHdr pList = sqlite3PcacheDirtyList(pPager.pPCache);
					PgHdr pPageOne = null;
					if (pList == null)
					{
						/* Must have at least one page for the WAL commit flag.
						** Ticket [2d1a5c67dfc2363e44f29d9bbd57f] 2null11-null5-18 */
						rc = sqlite3PagerGet(pPager, 1, ref pPageOne);
						pList = pPageOne;
						pList.pDirty = null;
					}
					Debug.Assert(rc == SQLITE_OK);
					if (ALWAYS(pList))
					{
						rc = pagerWalFrames(pPager, pList, pPager.dbSize, 1,
						(pPager.fullSync ? pPager.syncFlags : (byte)0)
						);
					}
					sqlite3PagerUnref(pPageOne);
					if (rc == SQLITE_OK)
					{
						sqlite3PcacheCleanAll(pPager.pPCache);
					}
				}
				else
				{
					/* The following block updates the change-counter. Exactly how it
					** does this depends on whether or not the atomic-update optimization
					** was enabled at compile time, and if this transaction meets the
					** runtime criteria to use the operation:
					**
					**    * The file-system supports the atomic-write property for
					**      blocks of size page-size, and
					**    * This commit is not part of a multi-file transaction, and
					**    * Exactly one page has been modified and store in the journal file.
					**
					** If the optimization was not enabled at compile time, then the
					** pager_incr_changecounter() function is called to update the change
					** counter in 'indirect-mode'. If the optimization is compiled in but
					** is not applicable to this transaction, call sqlite3JournalCreate()
					** to make sure the journal file has actually been created, then call
					** pager_incr_changecounter() to update the change-counter in indirect
					** mode.
					**
					** Otherwise, if the optimization is both enabled and applicable,
					** then call pager_incr_changecounter() to update the change-counter
					** in 'direct' mode. In this case the journal file will never be
					** created for this transaction.
					*/
#if SQLITE_ENABLE_ATOMIC_WRITE
PgHdr *pPg;
Debug.Assert( isOpen(pPager.jfd)
|| pPager.journalMode==PAGER_JOURNALMODE_OFF
|| pPager.journalMode==PAGER_JOURNALMODE_WAL
);
if( !zMaster && isOpen(pPager.jfd)
&& pPager.journalOff==jrnlBufferSize(pPager)
&& pPager.dbSize>=pPager.dbOrigSize
&& (0==(pPg = sqlite3PcacheDirtyList(pPager.pPCache)) || 0==pPg.pDirty)
){
/* Update the db file change counter via the direct-write method. The
** following call will modify the in-memory representation of page 1
** to include the updated change counter and then write page 1
** directly to the database file. Because of the atomic-write
** property of the host file-system, this is safe.
*/
rc = pager_incr_changecounter(pPager, 1);
}else{
rc = sqlite3JournalCreate(pPager.jfd);
if( rc==SQLITE_OK ){
rc = pager_incr_changecounter(pPager, 0);
}
}
#else
					rc = pager_incr_changecounter(pPager, false);
#endif
					if (rc != SQLITE_OK)
						goto commit_phase_one_exit;

					/* If this transaction has made the database smaller, then all pages
					** being discarded by the truncation must be written to the journal
					** file. This can only happen in auto-vacuum mode.
					**
					** Before reading the pages with page numbers larger than the
					** current value of Pager.dbSize, set dbSize back to the value
					** that it took at the start of the transaction. Otherwise, the
					** calls to sqlite3PagerGet() return zeroed pages instead of
					** reading data from the database file.
					*/
#if !SQLITE_OMIT_AUTOVACUUM
					if (pPager.dbSize < pPager.dbOrigSize
					&& pPager.journalMode != PAGER_JOURNALMODE_OFF
					)
					{
						Pgno i;                                   /* Iterator variable */
						Pgno iSkip = PAGER_MJ_PGNO(pPager); /* Pending lock page */
						Pgno dbSize = pPager.dbSize;       /* Database image size */
						pPager.dbSize = pPager.dbOrigSize;
						for (i = dbSize + 1; i <= pPager.dbOrigSize; i++)
						{
							if (0 == sqlite3BitvecTest(pPager.pInJournal, i) && i != iSkip)
							{
								PgHdr pPage = null;             /* Page to journal */
								rc = sqlite3PagerGet(pPager, i, ref pPage);
								if (rc != SQLITE_OK)
									goto commit_phase_one_exit;
								rc = sqlite3PagerWrite(pPage);
								sqlite3PagerUnref(pPage);
								if (rc != SQLITE_OK)
									goto commit_phase_one_exit;
							}
						}
						pPager.dbSize = dbSize;
					}
#endif

					/* Write the master journal name into the journal file. If a master
** journal file name has already been written to the journal file,
** or if zMaster is NULL (no master journal), then this call is a no-op.
*/
					rc = writeMasterJournal(pPager, zMaster);
					if (rc != SQLITE_OK)
						goto commit_phase_one_exit;

					/* Sync the journal file and write all dirty pages to the database.
					** If the atomic-update optimization is being used, this sync will not
					** create the journal file or perform any real IO.
					**
					** Because the change-counter page was just modified, unless the
					** atomic-update optimization is used it is almost certain that the
					** journal requires a sync here. However, in locking_mode=exclusive
					** on a system under memory pressure it is just possible that this is
					** not the case. In this case it is likely enough that the redundant
					** xSync() call will be changed to a no-op by the OS anyhow.
					*/
					rc = syncJournal(pPager, 0);
					if (rc != SQLITE_OK)
						goto commit_phase_one_exit;

					rc = pager_write_pagelist(pPager, sqlite3PcacheDirtyList(pPager.pPCache));
					if (rc != SQLITE_OK)
					{
						Debug.Assert(rc != SQLITE_IOERR_BLOCKED);
						goto commit_phase_one_exit;
					}
					sqlite3PcacheCleanAll(pPager.pPCache);

					/* If the file on disk is not the same size as the database image,
					** then use pager_truncate to grow or shrink the file here.
					*/
					if (pPager.dbSize != pPager.dbFileSize)
					{
						Pgno nNew = (Pgno)(pPager.dbSize - (pPager.dbSize == PAGER_MJ_PGNO(pPager) ? 1 : 0));
						Debug.Assert(pPager.eState >= PAGER_WRITER_DBMOD);
						rc = pager_truncate(pPager, nNew);
						if (rc != SQLITE_OK)
							goto commit_phase_one_exit;
					}

					/* Finally, sync the database file. */
					if (!noSync)
					{
						rc = sqlite3PagerSync(pPager);
					}
					IOTRACE("DBSYNC %p\n", pPager);
				}
			}

		commit_phase_one_exit:
			if (rc == SQLITE_OK && !pagerUseWal(pPager))
			{
				pPager.eState = PAGER_WRITER_FINISHED;
			}
			return rc;
		}

		/*
		** When this function is called, the database file has been completely
		** updated to reflect the changes made by the current transaction and
		** synced to disk. The journal file still exists in the file-system
		** though, and if a failure occurs at this point it will eventually
		** be used as a hot-journal and the current transaction rolled back.
		**
		** This function finalizes the journal file, either by deleting,
		** truncating or partially zeroing it, so that it cannot be used
		** for hot-journal rollback. Once this is done the transaction is
		** irrevocably committed.
		**
		** If an error occurs, an IO error code is returned and the pager
		** moves into the error state. Otherwise, SQLITE_OK is returned.
		*/

		private static int sqlite3PagerCommitPhaseTwo(Pager pPager)
		{
			int rc = SQLITE_OK;                 /* Return code */

			/* This routine should not be called if a prior error has occurred.
			** But if (due to a coding error elsewhere in the system) it does get
			** called, just return the same error code without doing anything. */
			if (NEVER(pPager.errCode) != 0)
				return pPager.errCode;

			Debug.Assert(pPager.eState == PAGER_WRITER_LOCKED
			|| pPager.eState == PAGER_WRITER_FINISHED
			|| (pagerUseWal(pPager) && pPager.eState == PAGER_WRITER_CACHEMOD)
			);
			Debug.Assert(assert_pager_state(pPager));

			/* An optimization. If the database was not actually modified during
			** this transaction, the pager is running in exclusive-mode and is
			** using persistent journals, then this function is a no-op.
			**
			** The start of the journal file currently contains a single journal
			** header with the nRec field set to 0. If such a journal is used as
			** a hot-journal during hot-journal rollback, 0 changes will be made
			** to the database file. So there is no need to zero the journal
			** header. Since the pager is in exclusive mode, there is no need
			** to drop any locks either.
			*/
			if (pPager.eState == PAGER_WRITER_LOCKED
			&& pPager.exclusiveMode
			&& pPager.journalMode == PAGER_JOURNALMODE_PERSIST
			)
			{
				Debug.Assert(pPager.journalOff == JOURNAL_HDR_SZ(pPager) || 0 == pPager.journalOff);
				pPager.eState = PAGER_READER;
				return SQLITE_OK;
			}

			PAGERTRACE("COMMIT %d\n", PAGERID(pPager));
			rc = pager_end_transaction(pPager, pPager.setMaster);
			return pager_error(pPager, rc);
		}

		/*
		** If a write transaction is open, then all changes made within the
		** transaction are reverted and the current write-transaction is closed.
		** The pager falls back to PAGER_READER state if successful, or PAGER_ERROR
		** state if an error occurs.
		**
		** If the pager is already in PAGER_ERROR state when this function is called,
		** it returns Pager.errCode immediately. No work is performed in this case.
		**
		** Otherwise, in rollback mode, this function performs two functions:
		**
		**   1) It rolls back the journal file, restoring all database file and
		**      in-memory cache pages to the state they were in when the transaction
		**      was opened, and
		**
		**   2) It finalizes the journal file, so that it is not used for hot
		**      rollback at any point in the future.
		**
		** Finalization of the journal file (task 2) is only performed if the
		** rollback is successful.
		**
		** In WAL mode, all cache-entries containing data modified within the
		** current transaction are either expelled from the cache or reverted to
		** their pre-transaction state by re-reading data from the database or
		** WAL files. The WAL transaction is then closed.
		*/

		private static int sqlite3PagerRollback(Pager pPager)
		{
			int rc = SQLITE_OK;                  /* Return code */
			PAGERTRACE("ROLLBACK %d\n", PAGERID(pPager));

			/* PagerRollback() is a no-op if called in READER or OPEN state. If
			** the pager is already in the ERROR state, the rollback is not
			** attempted here. Instead, the error code is returned to the caller.
			*/
			Debug.Assert(assert_pager_state(pPager));
			if (pPager.eState == PAGER_ERROR)
				return pPager.errCode;
			if (pPager.eState <= PAGER_READER)
				return SQLITE_OK;

			if (pagerUseWal(pPager))
			{
				int rc2;

				rc = sqlite3PagerSavepoint(pPager, SAVEPOINT_ROLLBACK, -1);
				rc2 = pager_end_transaction(pPager, pPager.setMaster);
				if (rc == SQLITE_OK)
					rc = rc2;
				rc = pager_error(pPager, rc);
			}
			else if (!isOpen(pPager.jfd) || pPager.eState == PAGER_WRITER_LOCKED)
			{
				int eState = pPager.eState;
				rc = pager_end_transaction(pPager, 0);
				if (
#if SQLITE_OMIT_MEMORYDB
0==MEMDB
#else
0 == pPager.memDb
#endif
 && eState > PAGER_WRITER_LOCKED)
				{
					/* This can happen using journal_mode=off. Move the pager to the error
					** state to indicate that the contents of the cache may not be trusted.
					** Any active readers will get SQLITE_ABORT.
					*/
					pPager.errCode = SQLITE_ABORT;
					pPager.eState = PAGER_ERROR;
					return rc;
				}
			}
			else
			{
				rc = pager_playback(pPager, 0);
			}

			Debug.Assert(pPager.eState == PAGER_READER || rc != SQLITE_OK);
			Debug.Assert(rc == SQLITE_OK || rc == SQLITE_FULL || (rc & 0xFF) == SQLITE_IOERR);

			/* If an error occurs during a ROLLBACK, we can no longer trust the pager
			** cache. So call pager_error() on the way out to make any error persistent.
			*/
			return pager_error(pPager, rc);
		}

		/*
		** Return TRUE if the database file is opened read-only.  Return FALSE
		** if the database is (in theory) writable.
		*/

		private static bool sqlite3PagerIsreadonly(Pager pPager)
		{
			return pPager.readOnly;
		}

		/*
		** Return the number of references to the pager.
		*/

		private static int sqlite3PagerRefcount(Pager pPager)
		{
			return sqlite3PcacheRefCount(pPager.pPCache);
		}

		/*
		** Return the approximate number of bytes of memory currently
		** used by the pager and its associated cache.
		*/

		private static int sqlite3PagerMemUsed(Pager pPager)
		{
			int perPageSize = pPager.pageSize + pPager.nExtra + 20; //+ sizeof(PgHdr) + 5*sizeof(void*);
			return perPageSize * sqlite3PcachePagecount(pPager.pPCache)
			+ 0// Not readily available under C#// sqlite3MallocSize(pPager);
			+ pPager.pageSize;
		}

		/*
		** Return the number of references to the specified page.
		*/

		private static int sqlite3PagerPageRefcount(DbPage pPage)
		{
			return sqlite3PcachePageRefcount(pPage);
		}

#if SQLITE_TEST
    /*
** This routine is used for testing and analysis only.
*/
    static int[] sqlite3PagerStats( Pager pPager )
    {
      int[] a = new int[11];
      a[0] = sqlite3PcacheRefCount( pPager.pPCache );
      a[1] = sqlite3PcachePagecount( pPager.pPCache );
      a[2] = sqlite3PcacheGetCachesize( pPager.pPCache );
      a[3] = pPager.eState == PAGER_OPEN ? -1 : (int)pPager.dbSize;
      a[4] = pPager.eState;
      a[5] = pPager.errCode;
      a[6] = pPager.nHit;
      a[7] = pPager.nMiss;
      a[8] = 0;  /* Used to be pPager.nOvfl */
      a[9] = pPager.nRead;
      a[10] = pPager.nWrite;
      return a;
    }
#endif

		/*
** Return true if this is an in-memory pager.
*/

		private static bool sqlite3PagerIsMemdb(Pager pPager)
		{
#if SQLITE_OMIT_MEMORYDB
return MEMDB != 0;
#else
			return pPager.memDb != 0;
#endif
		}

		/*
		** Check that there are at least nSavepoint savepoints open. If there are
		** currently less than nSavepoints open, then open one or more savepoints
		** to make up the difference. If the number of savepoints is already
		** equal to nSavepoint, then this function is a no-op.
		**
		** If a memory allocation fails, SQLITE_NOMEM is returned. If an error
		** occurs while opening the sub-journal file, then an IO error code is
		** returned. Otherwise, SQLITE_OK.
		*/

		private static int sqlite3PagerOpenSavepoint(Pager pPager, int nSavepoint)
		{
			int rc = SQLITE_OK;                      /* Return code */
			int nCurrent = pPager.nSavepoint;        /* Current number of savepoints */

			Debug.Assert(pPager.eState >= PAGER_WRITER_LOCKED);
			Debug.Assert(assert_pager_state(pPager));

			if (nSavepoint > nCurrent && pPager.useJournal != 0)
			{
				int ii;                 /* Iterator variable */
				PagerSavepoint[] aNew;  /* New Pager.aSavepoint array */

				/* Grow the Pager.aSavepoint array using realloc(). Return SQLITE_NOMEM
				** if the allocation fails. Otherwise, zero the new portion in case a
				** malloc failure occurs while populating it in the for(...) loop below.
				*/
				//aNew = (PagerSavepoint *)sqlite3Realloc(
				//    pPager.aSavepoint, sizeof(PagerSavepoint)*nSavepoint
				//);
				Array.Resize(ref pPager.aSavepoint, nSavepoint);
				aNew = pPager.aSavepoint;
				//if( null==aNew ){
				//  return SQLITE_NOMEM;
				//}
				// memset(&aNew[nCurrent], 0, (nSavepoint-nCurrent) * sizeof(PagerSavepoint));
				// pPager.aSavepoint = aNew;

				/* Populate the PagerSavepoint structures just allocated. */
				for (ii = nCurrent; ii < nSavepoint; ii++)
				{
					aNew[ii] = new PagerSavepoint();
					aNew[ii].nOrig = pPager.dbSize;
					if (isOpen(pPager.jfd) && pPager.journalOff > 0)
					{
						aNew[ii].iOffset = pPager.journalOff;
					}
					else
					{
						aNew[ii].iOffset = (int)JOURNAL_HDR_SZ(pPager);
					}
					aNew[ii].iSubRec = pPager.nSubRec;
					aNew[ii].pInSavepoint = sqlite3BitvecCreate(pPager.dbSize);
					//if ( null == aNew[ii].pInSavepoint )
					//{
					//  return SQLITE_NOMEM;
					//}
					if (pagerUseWal(pPager))
					{
						sqlite3WalSavepoint(pPager.pWal, aNew[ii].aWalData);
					}
					pPager.nSavepoint = ii + 1;
				}
				Debug.Assert(pPager.nSavepoint == nSavepoint);
				assertTruncateConstraint(pPager);
			}

			return rc;
		}

		/*
		** This function is called to rollback or release (commit) a savepoint.
		** The savepoint to release or rollback need not be the most recently
		** created savepoint.
		**
		** Parameter op is always either SAVEPOINT_ROLLBACK or SAVEPOINT_RELEASE.
		** If it is SAVEPOINT_RELEASE, then release and destroy the savepoint with
		** index iSavepoint. If it is SAVEPOINT_ROLLBACK, then rollback all changes
		** that have occurred since the specified savepoint was created.
		**
		** The savepoint to rollback or release is identified by parameter
		** iSavepoint. A value of 0 means to operate on the outermost savepoint
		** (the first created). A value of (Pager.nSavepoint-1) means operate
		** on the most recently created savepoint. If iSavepoint is greater than
		** (Pager.nSavepoint-1), then this function is a no-op.
		**
		** If a negative value is passed to this function, then the current
		** transaction is rolled back. This is different to calling
		** sqlite3PagerRollback() because this function does not terminate
		** the transaction or unlock the database, it just restores the
		** contents of the database to its original state.
		**
		** In any case, all savepoints with an index greater than iSavepoint
		** are destroyed. If this is a release operation (op==SAVEPOINT_RELEASE),
		** then savepoint iSavepoint is also destroyed.
		**
		** This function may return SQLITE_NOMEM if a memory allocation fails,
		** or an IO error code if an IO error occurs while rolling back a
		** savepoint. If no errors occur, SQLITE_OK is returned.
		*/

		private static int sqlite3PagerSavepoint(Pager pPager, int op, int iSavepoint)
		{
			int rc = pPager.errCode;       /* Return code */

			Debug.Assert(op == SAVEPOINT_RELEASE || op == SAVEPOINT_ROLLBACK);
			Debug.Assert(iSavepoint >= 0 || op == SAVEPOINT_ROLLBACK);

			if (rc == SQLITE_OK && iSavepoint < pPager.nSavepoint)
			{
				int ii;        /* Iterator variable */
				int nNew;      /* Number of remaining savepoints after this op. */

				/* Figure out how many savepoints will still be active after this
				** operation. Store this value in nNew. Then free resources associated
				** with any savepoints that are destroyed by this operation.
				*/
				nNew = iSavepoint + ((op == SAVEPOINT_RELEASE) ? 0 : 1);
				for (ii = nNew; ii < pPager.nSavepoint; ii++)
				{
					sqlite3BitvecDestroy(ref pPager.aSavepoint[ii].pInSavepoint);
				}
				pPager.nSavepoint = nNew;

				/* If this is a release of the outermost savepoint, truncate
				** the sub-journal to zero bytes in size. */
				if (op == SAVEPOINT_RELEASE)
				{
					if (nNew == 0 && isOpen(pPager.sjfd))
					{
						/* Only truncate if it is an in-memory sub-journal. */
						if (sqlite3IsMemJournal(pPager.sjfd))
						{
							rc = sqlite3OsTruncate(pPager.sjfd, 0);
							Debug.Assert(rc == SQLITE_OK);
						}
						pPager.nSubRec = 0;
					}
				}
				/* Else this is a rollback operation, playback the specified savepoint.
				** If this is a temp-file, it is possible that the journal file has
				** not yet been opened. In this case there have been no changes to
				** the database file, so the playback operation can be skipped.
				*/
				else if (pagerUseWal(pPager) || isOpen(pPager.jfd))
				{
					PagerSavepoint pSavepoint = (nNew == 0) ? null : pPager.aSavepoint[nNew - 1];
					rc = pagerPlaybackSavepoint(pPager, pSavepoint);
					Debug.Assert(rc != SQLITE_DONE);
				}
			}
			return rc;
		}

		/*
		** Return the full pathname of the database file.
		*/

		private static string sqlite3PagerFilename(Pager pPager)
		{
			return pPager.zFilename;
		}

		/*
		** Return the VFS structure for the pager.
		*/

		private static sqlite3_vfs sqlite3PagerVfs(Pager pPager)
		{
			return pPager.pVfs;
		}

		/*
		** Return the file handle for the database file associated
		** with the pager.  This might return NULL if the file has
		** not yet been opened.
		*/

		private static sqlite3_file sqlite3PagerFile(Pager pPager)
		{
			return pPager.fd;
		}

		/*
		** Return the full pathname of the journal file.
		*/

		private static string sqlite3PagerJournalname(Pager pPager)
		{
			return pPager.zJournal;
		}

		/*
		** Return true if fsync() calls are disabled for this pager.  Return FALSE
		** if fsync()s are executed normally.
		*/

		private static bool sqlite3PagerNosync(Pager pPager)
		{
			return pPager.noSync;
		}

#if SQLITE_HAS_CODEC
		/*
** Set or retrieve the codec for this pager
*/

		private static void sqlite3PagerSetCodec(
		Pager pPager,
		dxCodec xCodec,                 //void *(*xCodec)(void*,void*,Pgno,int),
		dxCodecSizeChng xCodecSizeChng, //void (*xCodecSizeChng)(void*,int,int),
		dxCodecFree xCodecFree,         //void (*xCodecFree)(void*),
		codec_ctx pCodec
		)
		{
			if (pPager.xCodecFree != null)
				pPager.xCodecFree(ref pPager.pCodec);
			pPager.xCodec = (pPager.memDb != 0) ? null : xCodec;
			pPager.xCodecSizeChng = xCodecSizeChng;
			pPager.xCodecFree = xCodecFree;
			pPager.pCodec = pCodec;
			pagerReportSize(pPager);
		}

		private static object sqlite3PagerGetCodec(Pager pPager)
		{
			return pPager.pCodec;
		}

#endif

#if !SQLITE_OMIT_AUTOVACUUM
		/*
** Move the page pPg to location pgno in the file.
**
** There must be no references to the page previously located at
** pgno (which we call pPgOld) though that page is allowed to be
** in cache.  If the page previously located at pgno is not already
** in the rollback journal, it is not put there by by this routine.
**
** References to the page pPg remain valid. Updating any
** meta-data associated with pPg (i.e. data stored in the nExtra bytes
** allocated along with the page) is the responsibility of the caller.
**
** A transaction must be active when this routine is called. It used to be
** required that a statement transaction was not active, but this restriction
** has been removed (CREATE INDEX needs to move a page when a statement
** transaction is active).
**
** If the fourth argument, isCommit, is non-zero, then this page is being
** moved as part of a database reorganization just before the transaction
** is being committed. In this case, it is guaranteed that the database page
** pPg refers to will not be written to again within this transaction.
**
** This function may return SQLITE_NOMEM or an IO error code if an error
** occurs. Otherwise, it returns SQLITE_OK.
*/

		private static int sqlite3PagerMovepage(Pager pPager, DbPage pPg, u32 pgno, int isCommit)
		{
			PgHdr pPgOld;                /* The page being overwritten. */
			u32 needSyncPgno = 0;        /* Old value of pPg.pgno, if sync is required */
			int rc;                      /* Return code */
			Pgno origPgno;               /* The original page number */

			Debug.Assert(pPg.nRef > 0);
			Debug.Assert(pPager.eState == PAGER_WRITER_CACHEMOD
			|| pPager.eState == PAGER_WRITER_DBMOD
			);
			Debug.Assert(assert_pager_state(pPager));

			/* In order to be able to rollback, an in-memory database must journal
			** the page we are moving from.
			*/
			if (
#if SQLITE_OMIT_MEMORYDB
1==MEMDB
#else
pPager.memDb != 0
#endif
)
			{
				rc = sqlite3PagerWrite(pPg);
				if (rc != 0)
					return rc;
			}

			/* If the page being moved is dirty and has not been saved by the latest
			** savepoint, then save the current contents of the page into the
			** sub-journal now. This is required to handle the following scenario:
			**
			**   BEGIN;
			**     <journal page X, then modify it in memory>
			**     SAVEPOINT one;
			**       <Move page X to location Y>
			**     ROLLBACK TO one;
			**
			** If page X were not written to the sub-journal here, it would not
			** be possible to restore its contents when the "ROLLBACK TO one"
			** statement were is processed.
			**
			** subjournalPage() may need to allocate space to store pPg.pgno into
			** one or more savepoint bitvecs. This is the reason this function
			** may return SQLITE_NOMEM.
			*/
			if ((pPg.flags & PGHDR_DIRTY) != 0
			&& subjRequiresPage(pPg)
			&& SQLITE_OK != (rc = subjournalPage(pPg))
			)
			{
				return rc;
			}

			PAGERTRACE("MOVE %d page %d (needSync=%d) moves to %d\n",
			PAGERID(pPager), pPg.pgno, (pPg.flags & PGHDR_NEED_SYNC) != 0 ? 1 : 0, pgno);
			IOTRACE("MOVE %p %d %d\n", pPager, pPg.pgno, pgno);

			/* If the journal needs to be sync()ed before page pPg.pgno can
			** be written to, store pPg.pgno in local variable needSyncPgno.
			**
			** If the isCommit flag is set, there is no need to remember that
			** the journal needs to be sync()ed before database page pPg.pgno
			** can be written to. The caller has already promised not to write to it.
			*/
			if (((pPg.flags & PGHDR_NEED_SYNC) != 0) && 0 == isCommit)
			{
				needSyncPgno = pPg.pgno;
				Debug.Assert(pageInJournal(pPg) || pPg.pgno > pPager.dbOrigSize);
				Debug.Assert((pPg.flags & PGHDR_DIRTY) != 0);
			}

			/* If the cache contains a page with page-number pgno, remove it
			** from its hash chain. Also, if the PGHDR_NEED_SYNC was set for
			** page pgno before the 'move' operation, it needs to be retained
			** for the page moved there.
			*/
			pPg.flags &= ~PGHDR_NEED_SYNC;
			pPgOld = pager_lookup(pPager, pgno);
			Debug.Assert(null == pPgOld || pPgOld.nRef == 1);
			if (pPgOld != null)
			{
				pPg.flags |= (pPgOld.flags & PGHDR_NEED_SYNC);
				if (
#if SQLITE_OMIT_MEMORYDB
1==MEMDB
#else
pPager.memDb != 0
#endif
)
				{
					/* Do not discard pages from an in-memory database since we might
					** need to rollback later.  Just move the page out of the way. */
					sqlite3PcacheMove(pPgOld, pPager.dbSize + 1);
				}
				else
				{
					sqlite3PcacheDrop(pPgOld);
				}
			}
			origPgno = pPg.pgno;
			sqlite3PcacheMove(pPg, pgno);
			sqlite3PcacheMakeDirty(pPg);

			/* For an in-memory database, make sure the original page continues
			** to exist, in case the transaction needs to roll back.  Use pPgOld
			** as the original page since it has already been allocated.
			*/
			if (
#if SQLITE_OMIT_MEMORYDB
0!=MEMDB
#else
0 != pPager.memDb
#endif
)
			{
				Debug.Assert(pPgOld);
				sqlite3PcacheMove(pPgOld, origPgno);
				sqlite3PagerUnref(pPgOld);
			}

			if (needSyncPgno != 0)
			{
				/* If needSyncPgno is non-zero, then the journal file needs to be
				** sync()ed before any data is written to database file page needSyncPgno.
				** Currently, no such page exists in the page-cache and the
				** "is journaled" bitvec flag has been set. This needs to be remedied by
				** loading the page into the pager-cache and setting the PGHDR_NEED_SYNC
				** flag.
				**
				** If the attempt to load the page into the page-cache fails, (due
				** to a malloc() or IO failure), clear the bit in the pInJournal[]
				** array. Otherwise, if the page is loaded and written again in
				** this transaction, it may be written to the database file before
				** it is synced into the journal file. This way, it may end up in
				** the journal file twice, but that is not a problem.
				*/
				PgHdr pPgHdr = null;
				rc = sqlite3PagerGet(pPager, needSyncPgno, ref pPgHdr);
				if (rc != SQLITE_OK)
				{
					if (needSyncPgno <= pPager.dbOrigSize)
					{
						Debug.Assert(pPager.pTmpSpace != null);
						u32[] pTemp = new u32[pPager.pTmpSpace.Length];
						sqlite3BitvecClear(pPager.pInJournal, needSyncPgno, pTemp);//pPager.pTmpSpace );
					}
					return rc;
				}
				pPgHdr.flags |= PGHDR_NEED_SYNC;
				sqlite3PcacheMakeDirty(pPgHdr);
				sqlite3PagerUnref(pPgHdr);
			}
			return SQLITE_OK;
		}

#endif

		/*
** Return a pointer to the data for the specified page.
*/

		private static byte[] sqlite3PagerGetData(DbPage pPg)
		{
			Debug.Assert(pPg.nRef > 0 || pPg.pPager.memDb != 0);
			return pPg.pData;
		}

		/*
		** Return a pointer to the Pager.nExtra bytes of "extra" space
		** allocated along with the specified page.
		*/

		private static MemPage sqlite3PagerGetExtra(DbPage pPg)
		{
			return pPg.pExtra;
		}

		/*
		** Get/set the locking-mode for this pager. Parameter eMode must be one
		** of PAGER_LOCKINGMODE_QUERY, PAGER_LOCKINGMODE_NORMAL or
		** PAGER_LOCKINGMODE_EXCLUSIVE. If the parameter is not _QUERY, then
		** the locking-mode is set to the value specified.
		**
		** The returned value is either PAGER_LOCKINGMODE_NORMAL or
		** PAGER_LOCKINGMODE_EXCLUSIVE, indicating the current (possibly updated)
		** locking-mode.
		*/

		private static bool sqlite3PagerLockingMode(Pager pPager, int eMode)
		{
			Debug.Assert(eMode == PAGER_LOCKINGMODE_QUERY
			|| eMode == PAGER_LOCKINGMODE_NORMAL
			|| eMode == PAGER_LOCKINGMODE_EXCLUSIVE);
			Debug.Assert(PAGER_LOCKINGMODE_QUERY < 0);
			Debug.Assert(PAGER_LOCKINGMODE_NORMAL >= 0 && PAGER_LOCKINGMODE_EXCLUSIVE >= 0);
			Debug.Assert(pPager.exclusiveMode || false == sqlite3WalHeapMemory(pPager.pWal));
			if (eMode >= 0 && !pPager.tempFile && !sqlite3WalHeapMemory(pPager.pWal))
			{
				pPager.exclusiveMode = eMode != 0;
			}
			return pPager.exclusiveMode;
		}

		/*
		** Set the journal-mode for this pager. Parameter eMode must be one of:
		**
		**    PAGER_JOURNALMODE_DELETE
		**    PAGER_JOURNALMODE_TRUNCATE
		**    PAGER_JOURNALMODE_PERSIST
		**    PAGER_JOURNALMODE_OFF
		**    PAGER_JOURNALMODE_MEMORY
		**    PAGER_JOURNALMODE_WAL
		**
		** The journalmode is set to the value specified if the change is allowed.
		** The change may be disallowed for the following reasons:
		**
		**   *  An in-memory database can only have its journal_mode set to _OFF
		**      or _MEMORY.
		**
		**   *  Temporary databases cannot have _WAL journalmode.
		**
		** The returned indicate the current (possibly updated) journal-mode.
		*/

		private static int sqlite3PagerSetJournalMode(Pager pPager, int eMode)
		{
			u8 eOld = pPager.journalMode;    /* Prior journalmode */

#if SQLITE_DEBUG
			/* The print_pager_state() routine is intended to be used by the debugger
** only.  We invoke it once here to suppress a compiler warning. */
			print_pager_state(pPager);
#endif

			/* The eMode parameter is always valid */
			Debug.Assert(eMode == PAGER_JOURNALMODE_DELETE
			|| eMode == PAGER_JOURNALMODE_TRUNCATE
			|| eMode == PAGER_JOURNALMODE_PERSIST
			|| eMode == PAGER_JOURNALMODE_OFF
			|| eMode == PAGER_JOURNALMODE_WAL
			|| eMode == PAGER_JOURNALMODE_MEMORY);

			/* This routine is only called from the OP_JournalMode opcode, and
			** the logic there will never allow a temporary file to be changed
			** to WAL mode.
			*/
			Debug.Assert(pPager.tempFile == false || eMode != PAGER_JOURNALMODE_WAL);

			/* Do allow the journalmode of an in-memory database to be set to
			** anything other than MEMORY or OFF
			*/
			if (
#if SQLITE_OMIT_MEMORYDB
1==MEMDB
#else
1 == pPager.memDb
#endif
)
			{
				Debug.Assert(eOld == PAGER_JOURNALMODE_MEMORY || eOld == PAGER_JOURNALMODE_OFF);
				if (eMode != PAGER_JOURNALMODE_MEMORY && eMode != PAGER_JOURNALMODE_OFF)
				{
					eMode = eOld;
				}
			}

			if (eMode != eOld)
			{
				/* Change the journal mode. */
				Debug.Assert(pPager.eState != PAGER_ERROR);
				pPager.journalMode = (u8)eMode;

				/* When transistioning from TRUNCATE or PERSIST to any other journal
				** mode except WAL, unless the pager is in locking_mode=exclusive mode,
				** delete the journal file.
				*/
				Debug.Assert((PAGER_JOURNALMODE_TRUNCATE & 5) == 1);
				Debug.Assert((PAGER_JOURNALMODE_PERSIST & 5) == 1);
				Debug.Assert((PAGER_JOURNALMODE_DELETE & 5) == 0);
				Debug.Assert((PAGER_JOURNALMODE_MEMORY & 5) == 4);
				Debug.Assert((PAGER_JOURNALMODE_OFF & 5) == 0);
				Debug.Assert((PAGER_JOURNALMODE_WAL & 5) == 5);

				Debug.Assert(isOpen(pPager.fd) || pPager.exclusiveMode);
				if (!pPager.exclusiveMode && (eOld & 5) == 1 && (eMode & 1) == 0)
				{
					/* In this case we would like to delete the journal file. If it is
					** not possible, then that is not a problem. Deleting the journal file
					** here is an optimization only.
					**
					** Before deleting the journal file, obtain a RESERVED lock on the
					** database file. This ensures that the journal file is not deleted
					** while it is in use by some other client.
					*/
					sqlite3OsClose(pPager.jfd);
					if (pPager.eLock >= RESERVED_LOCK)
					{
						sqlite3OsDelete(pPager.pVfs, pPager.zJournal, 0);
					}
					else
					{
						int rc = SQLITE_OK;
						int state = pPager.eState;
						Debug.Assert(state == PAGER_OPEN || state == PAGER_READER);
						if (state == PAGER_OPEN)
						{
							rc = sqlite3PagerSharedLock(pPager);
						}
						if (pPager.eState == PAGER_READER)
						{
							Debug.Assert(rc == SQLITE_OK);
							rc = pagerLockDb(pPager, RESERVED_LOCK);
						}
						if (rc == SQLITE_OK)
						{
							sqlite3OsDelete(pPager.pVfs, pPager.zJournal, 0);
						}
						if (rc == SQLITE_OK && state == PAGER_READER)
						{
							pagerUnlockDb(pPager, SHARED_LOCK);
						}
						else if (state == PAGER_OPEN)
						{
							pager_unlock(pPager);
						}
						Debug.Assert(state == pPager.eState);
					}
				}
			}

			/* Return the new journal mode */
			return (int)pPager.journalMode;
		}

		/*
		** Return the current journal mode.
		*/

		private static int sqlite3PagerGetJournalMode(Pager pPager)
		{
			return (int)pPager.journalMode;
		}

		/*
		** Return TRUE if the pager is in a state where it is OK to change the
		** journalmode.  Journalmode changes can only happen when the database
		** is unmodified.
		*/

		private static int sqlite3PagerOkToChangeJournalMode(Pager pPager)
		{
			Debug.Assert(assert_pager_state(pPager));
			if (pPager.eState >= PAGER_WRITER_CACHEMOD)
				return 0;
			if (NEVER(isOpen(pPager.jfd) && pPager.journalOff > 0))
				return 0;
			return 1;
		}

		/*
		** Get/set the size-limit used for persistent journal files.
		**
		** Setting the size limit to -1 means no limit is enforced.
		** An attempt to set a limit smaller than -1 is a no-op.
		*/

		private static i64 sqlite3PagerJournalSizeLimit(Pager pPager, i64 iLimit)
		{
			if (iLimit >= -1)
			{
				pPager.journalSizeLimit = iLimit;
				sqlite3WalLimit(pPager.pWal, iLimit);
			}
			return pPager.journalSizeLimit;
		}

		/*
		** Return a pointer to the pPager.pBackup variable. The backup module
		** in backup.c maintains the content of this variable. This module
		** uses it opaquely as an argument to sqlite3BackupRestart() and
		** sqlite3BackupUpdate() only.
		*/

		private static sqlite3_backup sqlite3PagerBackupPtr(Pager pPager)
		{
			return pPager.pBackup;
		}

#if !SQLITE_OMIT_WAL
/*
** This function is called when the user invokes "PRAGMA wal_checkpoint",
** "PRAGMA wal_blocking_checkpoint" or calls the sqlite3_wal_checkpoint()
** or wal_blocking_checkpoint() API functions.
**
** Parameter eMode is one of SQLITE_CHECKPOINT_PASSIVE, FULL or RESTART.
*/
int sqlite3PagerCheckpoint(Pager *pPager, int eMode, int *pnLog, int *pnCkpt){
  int rc = SQLITE_OK;
  if( pPager.pWal ){
    rc = sqlite3WalCheckpoint(pPager.pWal, eMode,
        pPager.xBusyHandler, pPager.pBusyHandlerArg,
        pPager.ckptSyncFlags, pPager.pageSize, (u8 *)pPager.pTmpSpace,
        pnLog, pnCkpt
    );
  }
  return rc;
}

    int sqlite3PagerWalCallback(Pager *pPager){
return sqlite3WalCallback(pPager.pWal);
}

/*
** Return true if the underlying VFS for the given pager supports the
** primitives necessary for write-ahead logging.
*/
int sqlite3PagerWalSupported(Pager *pPager){
const sqlite3_io_methods *pMethods = pPager.fd->pMethods;
return pPager.exclusiveMode || (pMethods->iVersion>=2 && pMethods->xShmMap);
}

/*
** Attempt to take an exclusive lock on the database file. If a PENDING lock
** is obtained instead, immediately release it.
*/
static int pagerExclusiveLock(Pager *pPager){
int rc;                         /* Return code */

assert( pPager.eLock==SHARED_LOCK || pPager.eLock==EXCLUSIVE_LOCK );
rc = pagerLockDb(pPager, EXCLUSIVE_LOCK);
if( rc!=SQLITE_OK ){
/* If the attempt to grab the exclusive lock failed, release the
** pending lock that may have been obtained instead.  */
pagerUnlockDb(pPager, SHARED_LOCK);
}

return rc;
}

/*
** Call sqlite3WalOpen() to open the WAL handle. If the pager is in
** exclusive-locking mode when this function is called, take an EXCLUSIVE
** lock on the database file and use heap-memory to store the wal-index
** in. Otherwise, use the normal shared-memory.
*/
static int pagerOpenWal(Pager *pPager){
int rc = SQLITE_OK;

assert( pPager.pWal==0 && pPager.tempFile==0 );
assert( pPager.eLock==SHARED_LOCK || pPager.eLock==EXCLUSIVE_LOCK || pPager.noReadlock);

/* If the pager is already in exclusive-mode, the WAL module will use
** heap-memory for the wal-index instead of the VFS shared-memory
** implementation. Take the exclusive lock now, before opening the WAL
** file, to make sure this is safe.
*/
if( pPager.exclusiveMode ){
rc = pagerExclusiveLock(pPager);
}

/* Open the connection to the log file. If this operation fails,
** (e.g. due to malloc() failure), return an error code.
*/
if( rc==SQLITE_OK ){
rc = sqlite3WalOpen(pPager.pVfs,
pPager.fd, pPager.zWal, pPager.exclusiveMode, &pPager.pWal
        pPager.journalSizeLimit, &pPager.pWal
);
}

return rc;
}

/*
** The caller must be holding a SHARED lock on the database file to call
** this function.
**
** If the pager passed as the first argument is open on a real database
** file (not a temp file or an in-memory database), and the WAL file
** is not already open, make an attempt to open it now. If successful,
** return SQLITE_OK. If an error occurs or the VFS used by the pager does
** not support the xShmXXX() methods, return an error code. *pbOpen is
** not modified in either case.
**
** If the pager is open on a temp-file (or in-memory database), or if
** the WAL file is already open, set *pbOpen to 1 and return SQLITE_OK
** without doing anything.
*/
int sqlite3PagerOpenWal(
Pager *pPager,                  /* Pager object */
int *pbOpen                     /* OUT: Set to true if call is a no-op */
){
int rc = SQLITE_OK;             /* Return code */

assert( assert_pager_state(pPager) );
assert( pPager.eState==PAGER_OPEN   || pbOpen );
assert( pPager.eState==PAGER_READER || !pbOpen );
assert( pbOpen==0 || *pbOpen==0 );
assert( pbOpen!=0 || (!pPager.tempFile && !pPager.pWal) );

if( !pPager.tempFile && !pPager.pWal ){
if( !sqlite3PagerWalSupported(pPager) ) return SQLITE_CANTOPEN;

/* Close any rollback journal previously open */
sqlite3OsClose(pPager.jfd);

rc = pagerOpenWal(pPager);
if( rc==SQLITE_OK ){
pPager.journalMode = PAGER_JOURNALMODE_WAL;
pPager.eState = PAGER_OPEN;
}
}else{
*pbOpen = 1;
}

return rc;
}

/*
** This function is called to close the connection to the log file prior
** to switching from WAL to rollback mode.
**
** Before closing the log file, this function attempts to take an
** EXCLUSIVE lock on the database file. If this cannot be obtained, an
** error (SQLITE_BUSY) is returned and the log connection is not closed.
** If successful, the EXCLUSIVE lock is not released before returning.
*/
int sqlite3PagerCloseWal(Pager *pPager){
int rc = SQLITE_OK;

assert( pPager.journalMode==PAGER_JOURNALMODE_WAL );

/* If the log file is not already open, but does exist in the file-system,
** it may need to be checkpointed before the connection can switch to
** rollback mode. Open it now so this can happen.
*/
if( !pPager.pWal ){
int logexists = 0;
rc = pagerLockDb(pPager, SHARED_LOCK);
if( rc==SQLITE_OK ){
rc = sqlite3OsAccess(
pPager.pVfs, pPager.zWal, SQLITE_ACCESS_EXISTS, &logexists
);
}
if( rc==SQLITE_OK && logexists ){
rc = pagerOpenWal(pPager);
}
}

/* Checkpoint and close the log. Because an EXCLUSIVE lock is held on
** the database file, the log and log-summary files will be deleted.
*/
if( rc==SQLITE_OK && pPager.pWal ){
rc = pagerExclusiveLock(pPager);
if( rc==SQLITE_OK ){
rc = sqlite3WalClose(pPager.pWal, pPager.ckptSyncFlags,
           pPager.pageSize, (u8*)pPager.pTmpSpace);
pPager.pWal = 0;
}
}
return rc;
}

#if SQLITE_HAS_CODEC
/*
** This function is called by the wal module when writing page content
** into the log file.
**
** This function returns a pointer to a buffer containing the encrypted
** page content. If a malloc fails, this function may return NULL.
*/
void sqlite3PagerCodec(PgHdr *pPg){
voidaData = 0;
CODEC2(pPg->pPager, pPg->pData, pPg->pgno, 6, return 0, aData);
return aData;
}
#endif //* SQLITE_HAS_CODEC */

#endif //* !SQLITE_OMIT_WAL */

#endif // * SQLITE_OMIT_DISKIO */
	}
}